[librm] Reduce real-mode stack consumption in virt_call()
Some PXE NBPs are known to make PXE API calls with very little space available on the real-mode stack. For example, the Rembo-ia32 NBP from some versions of IBM's Tivoli Provisioning Manager for Operating System Deployment (TPMfOSD) will issue calls with the real-mode stack placed at 0000:03d2; this is at the end of the interrupt vector table and leaves only 498 bytes of stack space available before overwriting the hardware IRQ vectors. This limits the amount of state that we can preserve before transitioning to protected mode. Work around these challenging conditions by preserving everything other than the initial register dump in a temporary static buffer within our real-mode data segment, and copying the contents of this buffer to the protected-mode stack. Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
parent
b696a5063e
commit
2d42d3cff6
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@ -180,17 +180,49 @@ gdt_end:
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* to us.
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****************************************************************************
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*/
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.section ".bss.rm_sp", "aw", @nobits
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.section ".bss.rm_ss_sp", "aw", @nobits
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.globl rm_sp
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rm_sp: .word 0
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.section ".bss.rm_ss", "aw", @nobits
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.globl rm_ss
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rm_ss: .word 0
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.section ".data.pm_esp", "aw", @progbits
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pm_esp: .long VIRTUAL(_estack)
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/****************************************************************************
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* Temporary static data buffer
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*
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* This is used to reduce the amount of real-mode stack space consumed
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* during mode transitions, since we are sometimes called with very
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* little real-mode stack space available.
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****************************************************************************
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*/
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/* Temporary static buffer usage by virt_call */
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.struct 0
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VC_TMP_GDT: .space 6
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VC_TMP_IDT: .space 6
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VC_TMP_PAD: .space 4 /* for alignment */
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.if64
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VC_TMP_CR3: .space 4
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VC_TMP_CR4: .space 4
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VC_TMP_EMER: .space 8
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.endif
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VC_TMP_END:
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.previous
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/* Temporary static buffer usage by real_call */
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.struct 0
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RC_TMP_FUNCTION: .space 4
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RC_TMP_END:
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.previous
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/* Shared temporary static buffer */
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.section ".bss16.rm_tmpbuf", "aw", @nobits
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.align 16
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rm_tmpbuf:
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.space VC_TMP_END
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.size rm_tmpbuf, . - rm_tmpbuf
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/****************************************************************************
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* Virtual address offsets
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*
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@ -341,6 +373,7 @@ set_seg_base:
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*
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* Parameters:
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* %ecx : number of bytes to move from RM stack to PM stack
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* %edx : number of bytes to copy from RM temporary buffer to PM stack
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*
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****************************************************************************
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*/
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@ -361,14 +394,19 @@ real_to_prot:
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/* Add protected-mode return address to length of data to be copied */
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addw $4, %cx /* %ecx must be less than 64kB anyway */
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/* Real-mode %ss:%sp => %ebp:%edx and virtual address => %esi */
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xorl %ebp, %ebp
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movw %ss, %bp
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movzwl %sp, %edx
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movl %ebp, %eax
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/* Real-mode %ss:%sp => %ebp and virtual address => %esi */
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xorl %eax, %eax
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movw %ss, %ax
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shll $4, %eax
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addr32 leal (%eax,%edx), %esi
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movzwl %sp, %ebp
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addr32 leal (%eax,%ebp), %esi
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subl rm_virt_offset, %esi
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shll $12, %eax
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orl %eax, %ebp
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/* Real-mode data segment virtual address => %ebx */
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movl rm_data16, %ebx
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.if64 ; subl rm_virt_offset, %ebx ; .endif
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/* Load protected-mode global descriptor table */
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data32 lgdt gdtr
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@ -407,15 +445,20 @@ r2p_pmode:
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lidt VIRTUAL(idtr32)
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/* Record real-mode %ss:sp (after removal of data) */
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movw %bp, VIRTUAL(rm_ss)
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addl %ecx, %edx
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movw %dx, VIRTUAL(rm_sp)
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addl %ecx, %ebp
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movl %ebp, VIRTUAL(rm_sp)
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/* Move data from RM stack to PM stack */
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subl %edx, %esp
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subl %ecx, %esp
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movl %esp, %edi
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rep movsb
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/* Copy data from RM temporary buffer to PM stack */
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leal rm_tmpbuf(%ebx), %esi
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movl %edx, %ecx
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rep movsb
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/* Return to virtual address */
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ret
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@ -435,6 +478,7 @@ r2p_pmode:
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*
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* Parameters:
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* %ecx : number of bytes to move from PM stack to RM stack
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* %edx : number of bytes to move from PM stack to RM temporary buffer
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* %esi : real-mode global and interrupt descriptor table registers
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*
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****************************************************************************
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@ -455,19 +499,26 @@ prot_to_real:
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/* Add return address to data to be moved to RM stack */
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addl $4, %ecx
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/* Real-mode %ss:sp => %ebp:edx and virtual address => %edi */
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movzwl VIRTUAL(rm_ss), %ebp
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movzwl VIRTUAL(rm_sp), %edx
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subl %ecx, %edx
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movl %ebp, %eax
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/* Real-mode %ss:sp => %ebp and virtual address => %edi */
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movl VIRTUAL(rm_sp), %ebp
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subl %ecx, %ebp
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movzwl VIRTUAL(rm_ss), %eax
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shll $4, %eax
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leal (%eax,%edx), %edi
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movzwl %bp, %edi
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addl %eax, %edi
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subl VIRTUAL(virt_offset), %edi
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/* Move data from PM stack to RM stack */
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movl %esp, %esi
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rep movsb
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/* Move data from PM stack to RM temporary buffer */
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movl VIRTUAL(data16), %edi
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.if64 ; subl VIRTUAL(virt_offset), %edi ; .endif
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addl $rm_tmpbuf, %edi
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movl %edx, %ecx
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rep movsb
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/* Record protected-mode %esp (after removal of data) */
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movl %esi, VIRTUAL(pm_esp)
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@ -497,8 +548,10 @@ p2r_ljmp_rm_cs:
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movw %ax, %es
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movw %ax, %fs
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movw %ax, %gs
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movw %bp, %ss
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movl %edx, %esp
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movl %ebp, %eax
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shrl $16, %eax
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movw %ax, %ss
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movzwl %bp, %esp
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/* Return to real-mode address */
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data32 ret
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@ -921,14 +974,6 @@ long_restore_regs:
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****************************************************************************
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*/
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.struct 0
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VC_OFFSET_GDT: .space 6
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VC_OFFSET_IDT: .space 6
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.if64
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VC_OFFSET_PADDING64: .space 4 /* for alignment */
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VC_OFFSET_CR3: .space 4
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VC_OFFSET_CR4: .space 4
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VC_OFFSET_EMER: .space 8
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.endif
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VC_OFFSET_IX86: .space SIZEOF_I386_ALL_REGS
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VC_OFFSET_PADDING: .space 2 /* for alignment */
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VC_OFFSET_RETADDR: .space 2
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@ -941,7 +986,7 @@ VC_OFFSET_END:
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.code16
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.globl virt_call
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virt_call:
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/* Preserve registers, flags and GDT on external RM stack */
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/* Preserve registers and flags on external RM stack */
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pushw %ss /* padding */
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pushfl
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pushal
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@ -951,34 +996,38 @@ virt_call:
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pushw %ds
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pushw %ss
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pushw %cs
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subw $VC_OFFSET_IX86, %sp
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movw %sp, %bp
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sidt VC_OFFSET_IDT(%bp)
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sgdt VC_OFFSET_GDT(%bp)
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/* Claim ownership of temporary static buffer */
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cli
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/* Preserve GDT and IDT in temporary static buffer */
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movw %cs:rm_ds, %ds
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sidt ( rm_tmpbuf + VC_TMP_IDT )
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sgdt ( rm_tmpbuf + VC_TMP_GDT )
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.if64 ; /* Preserve control registers, if applicable */
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movl $MSR_EFER, %ecx
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rdmsr
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movl %eax, (VC_OFFSET_EMER+0)(%bp)
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movl %edx, (VC_OFFSET_EMER+4)(%bp)
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movl %eax, ( rm_tmpbuf + VC_TMP_EMER + 0 )
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movl %edx, ( rm_tmpbuf + VC_TMP_EMER + 4 )
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movl %cr4, %eax
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movl %eax, VC_OFFSET_CR4(%bp)
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movl %eax, ( rm_tmpbuf + VC_TMP_CR4 )
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movl %cr3, %eax
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movl %eax, VC_OFFSET_CR3(%bp)
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movl %eax, ( rm_tmpbuf + VC_TMP_CR3 )
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.endif
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/* For sanity's sake, clear the direction flag as soon as possible */
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cld
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/* Switch to protected mode and move register dump to PM stack */
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movl $VC_OFFSET_END, %ecx
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movl $VC_TMP_END, %edx
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pushl $VIRTUAL(vc_pmode)
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vc_jmp: jmp real_to_prot
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.section ".text.virt_call", "ax", @progbits
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.code32
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vc_pmode:
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/* Call function (in protected mode) */
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leal VC_OFFSET_IX86(%esp), %eax
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pushl %eax
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pushl %esp
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call *(VC_OFFSET_FUNCTION+4)(%esp)
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popl %eax /* discard */
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@ -989,11 +1038,9 @@ vc_lmode:
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.code64
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/* Call function (in long mode) */
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leaq VC_OFFSET_IX86(%rsp), %rdi
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pushq %rdi
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movslq (VC_OFFSET_FUNCTION+8)(%rsp), %rax
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movq %rsp, %rdi
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movslq VC_OFFSET_FUNCTION(%rsp), %rax
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callq *%rax
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popq %rdi /* discard */
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/* Switch to protected mode */
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call long_to_prot
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@ -1001,7 +1048,8 @@ vc_lmode:
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.endif
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/* Switch to real mode and move register dump back to RM stack */
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movl $VC_OFFSET_END, %ecx
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movl %esp, %esi
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movl $VC_TMP_END, %edx
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leal VC_TMP_GDT(%esp, %ecx), %esi
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pushl $vc_rmode
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jmp prot_to_real
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.section ".text16.virt_call", "ax", @progbits
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@ -1009,17 +1057,17 @@ vc_lmode:
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vc_rmode:
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.if64 ; /* Restore control registers, if applicable */
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movw %sp, %bp
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movl VC_OFFSET_CR3(%bp), %eax
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movl ( rm_tmpbuf + VC_TMP_CR3 ), %eax
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movl %eax, %cr3
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movl VC_OFFSET_CR4(%bp), %eax
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movl ( rm_tmpbuf + VC_TMP_CR4 ), %eax
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movl %eax, %cr4
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movl (VC_OFFSET_EMER+0)(%bp), %eax
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movl (VC_OFFSET_EMER+4)(%bp), %edx
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movl ( rm_tmpbuf + VC_TMP_EMER + 0 ), %eax
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movl ( rm_tmpbuf + VC_TMP_EMER + 4 ), %edx
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movl $MSR_EFER, %ecx
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wrmsr
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.endif
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/* Restore registers and flags and return */
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addw $( VC_OFFSET_IX86 + 4 /* also skip %cs and %ss */ ), %sp
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popl %eax /* skip %cs and %ss */
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popw %ds
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popw %es
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popw %fs
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@ -1067,6 +1115,7 @@ vc_rmode:
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.struct 0
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RC_OFFSET_REGS: .space SIZEOF_I386_REGS
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RC_OFFSET_REGS_END:
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RC_OFFSET_FUNCTION_COPY:.space 4
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.if64
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RC_OFFSET_LREGS: .space SIZEOF_X86_64_REGS
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RC_OFFSET_LREG_RETADDR: .space SIZEOF_ADDR
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@ -1087,11 +1136,12 @@ real_call:
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.code32
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.endif
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/* Create register dump and function pointer copy on PM stack */
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pushl ( RC_OFFSET_FUNCTION - RC_OFFSET_FUNCTION_COPY - 4 )(%esp)
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pushal
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pushl RC_OFFSET_FUNCTION(%esp)
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/* Switch to real mode and move register dump to RM stack */
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movl $( RC_OFFSET_REGS_END + 4 /* function pointer copy */ ), %ecx
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movl $RC_OFFSET_REGS_END, %ecx
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movl $RC_TMP_END, %edx
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pushl $rc_rmode
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movl $VIRTUAL(rm_default_gdtr_idtr), %esi
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jmp prot_to_real
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@ -1099,9 +1149,8 @@ real_call:
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.code16
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rc_rmode:
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/* Call real-mode function */
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popl rc_function
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popal
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call *rc_function
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call *( rm_tmpbuf + RC_TMP_FUNCTION )
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pushal
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/* For sanity's sake, clear the direction flag as soon as possible */
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@ -1109,6 +1158,7 @@ rc_rmode:
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/* Switch to protected mode and move register dump back to PM stack */
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movl $RC_OFFSET_REGS_END, %ecx
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xorl %edx, %edx
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pushl $VIRTUAL(rc_pmode)
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jmp real_to_prot
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.section ".text.real_call", "ax", @progbits
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@ -1126,12 +1176,6 @@ rc_pmode:
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ret $( RC_OFFSET_END - RC_OFFSET_PARAMS )
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/* Function vector, used because "call xx(%sp)" is not a valid
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* 16-bit expression.
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*/
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.section ".bss16.rc_function", "aw", @nobits
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rc_function: .word 0, 0
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/* Default real-mode global and interrupt descriptor table registers */
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.section ".data.rm_default_gdtr_idtr", "aw", @progbits
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rm_default_gdtr_idtr:
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