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[pxeprefix] Search for the PXE entry points through all methods
Search for the PXE entry points (via the !PXE or PXENV+ structures) through all known combinations of search methods. Furthermore, if we find a PXENV+ structure, attempt to use it to find the !PXE structure if at all possible.
This commit is contained in:
H. Peter Anvin
Michael Brown
parent
4dd746a725
commit
6a3f5d6db7
@ -31,18 +31,10 @@
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pushl $STACK_MAGIC
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movw %ss, %cs:pxe_ss
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movl %esp, %cs:pxe_esp
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movw %sp, %bp
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movl (10*4+4*2+4)(%bp),%ebp /* !PXE address */
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/* Set up %ds */
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/* Set up segments */
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movw %cs, %ax
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movw %ax, %ds
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/* Record PXENV+ and !PXE nominal addresses */
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movw %es, pxenv_segment /* PXENV+ address */
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movw %bx, pxenv_offset
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movl %ebp, ppxe_segoff /* !PXE address */
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/* Set up %es and %fs */
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movw %ax, %es
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movw $0x40, %ax /* BIOS data segment access */
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movw %ax, %fs
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/* Set up stack just below 0x7c00 */
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@ -60,16 +52,57 @@
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.previous
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/*****************************************************************************
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* Verify PXENV+ structure and record parameters of interest
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* Find us a usable !PXE or PXENV+ entry point
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*****************************************************************************
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*/
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detect_pxenv:
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/* Signature check */
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les pxenv_segoff, %bx
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cmpl $0x4e455850, %es:(%bx) /* 'PXEN' signature */
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jne no_pxenv
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cmpw $0x2b56, %es:4(%bx) /* 'V+' signature */
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jne no_pxenv
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detect_pxe:
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/* Plan A: !PXE pointer from the stack */
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lgsl pxe_esp, %ebp /* %gs:%bp -> original stack */
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lesw %gs:52(%bp), %bx
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call is_valid_ppxe
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je have_ppxe
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/* Plan B: PXENV+ pointer from initial ES:BX */
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movw %gs:32(%bp),%bx
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movw %gs:8(%bp),%es
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call is_valid_pxenv
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je have_pxenv
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/* Plan C: PXENV+ structure via INT 1Ah */
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movw $0x5650, %ax
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int $0x1a
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jc 1f
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cmpw $0x564e, %ax
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jne 1f
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call is_valid_pxenv
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je have_pxenv
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1:
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/* Plan D: scan base memory for !PXE */
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call memory_scan_ppxe
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je have_ppxe
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/* Plan E: scan base memory for PXENV+ */
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call memory_scan_pxenv
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jne stack_not_found
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have_pxenv:
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movw %bx, pxenv_offset
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movw %es, pxenv_segment
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cmpw $0x201, %es:6(%bx) /* API version >= 2.01 */
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jb 1f
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cmpb $0x2c, %es:8(%bx) /* ... and structure long enough */
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jb 2f
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lesw %es:0x28(%bx), %bx /* Find !PXE from PXENV+ */
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call is_valid_ppxe
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je have_ppxe
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2:
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call memory_scan_ppxe /* We are *supposed* to have !PXE... */
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je have_ppxe
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1:
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lesw pxenv_segoff, %bx /* Nope, we're stuck with PXENV+ */
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/* Record entry point and UNDI segments */
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pushl %es:0x0a(%bx) /* Entry point */
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popl entry_segoff
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@ -79,36 +112,22 @@ detect_pxenv:
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pushw %es:0x20(%bx) /* UNDI data segment */
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pushw %es:0x22(%bx) /* UNDI data size */
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popl undi_data_segoff
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/* Print "PXENV+ at <address>" */
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movw $10f, %si
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call print_message
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call print_segoff
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movb $( ',' ), %al
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call print_character
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jmp 99f
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jmp check_have_stack
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.section ".prefix.data", "aw", @progbits
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10: .asciz " PXENV+ at "
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.previous
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no_pxenv:
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xorl %eax, %eax
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movl %eax, pxenv_segoff
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99:
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/*****************************************************************************
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* Verify !PXE structure and record parameters of interest
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*****************************************************************************
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*/
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detect_ppxe:
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/* Signature check */
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les ppxe_segoff, %bx
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cmpl $0x45585021, %es:(%bx) /* '!PXE' signature */
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jne no_ppxe
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/* Record structure address, entry point, and UNDI segments */
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pushw %es
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popw ppxe_segment
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have_ppxe:
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movw %bx, ppxe_offset
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movw %es, ppxe_segment
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pushl %es:0x10(%bx) /* Entry point */
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popl entry_segoff
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pushw %es:0x30(%bx) /* UNDI code segment */
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@ -123,17 +142,60 @@ detect_ppxe:
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call print_segoff
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movb $( ',' ), %al
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call print_character
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jmp 99f
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jmp check_have_stack
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.section ".prefix.data", "aw", @progbits
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10: .asciz " !PXE at "
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.previous
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no_ppxe:
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xorl %eax, %eax
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movl %eax, ppxe_segoff
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is_valid_ppxe:
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cmpl $0x45585021, %es:(%bx)
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jne 1f
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movzbw %es:4(%bx), %cx
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cmpw $0x58, %cx
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jae is_valid_checksum
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1:
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ret
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is_valid_pxenv:
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cmpl $0x4e455850, %es:(%bx)
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jne 1b
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cmpw $0x2b56, %es:4(%bx)
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jne 1b
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movzbw %es:8(%bx), %cx
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cmpw $0x28, %cx
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jb 1b
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is_valid_checksum:
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pushw %ax
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movw %bx, %si
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xorw %ax, %ax
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2:
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es lodsb
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addb %al, %ah
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loopw 2b
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popw %ax
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ret
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99:
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memory_scan_ppxe:
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movw $is_valid_ppxe, %dx
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jmp memory_scan_common
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memory_scan_pxenv:
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movw $is_valid_pxenv, %dx
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memory_scan_common:
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movw %fs:(0x13), %ax
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shlw $6, %ax
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decw %ax
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1: incw %ax
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cmpw $( 0xa000 - 1 ), %ax
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ja 2f
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movw %ax, %es
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xorw %bx, %bx
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call *%dx
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jne 1b
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2: ret
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/*****************************************************************************
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* Sanity check: we must have an entry point
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*****************************************************************************
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@ -144,6 +206,7 @@ check_have_stack:
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testl %eax, %eax
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jnz 99f
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/* No entry point: print message and skip everything else */
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stack_not_found:
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movw $10f, %si
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call print_message
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jmp finished
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@ -529,8 +592,8 @@ print_pxe_error:
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*/
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.section ".prefix.data"
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pxe_ss: .word 0
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pxe_esp: .long 0
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pxe_ss: .word 0
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pxe_parameter_structure: .fill 20
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