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Subject[PATCH 01/20] efi/libstub: fix boot argument handling in mixed mode entry code
Date
The mixed mode refactor actually broke mixed mode by failing to
pass the bootparam structure to startup_32(). This went unnoticed
because it apparently has a high tolerance for being passed random
junk, and still boots fine in some cases. So let's fix this by
populating %esi as required when entering via efi32_stub_entry,
and while at it, preserve the arguments themselves instead of their
address in memory (via the stack pointer) since that memory could
be clobbered before we get to it.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/x86/boot/compressed/head_64.S | 17 ++++++++++-------
1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index a6f3ee9ca61d..44a6bb6964b5 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -208,13 +208,12 @@ SYM_FUNC_START(startup_32)
pushl $__KERNEL_CS
leal startup_64(%ebp), %eax
#ifdef CONFIG_EFI_MIXED
- movl efi32_boot_args(%ebp), %ebx
- cmp $0, %ebx
+ movl efi32_boot_args(%ebp), %edi
+ cmp $0, %edi
jz 1f
leal handover_entry(%ebp), %eax
- movl 0(%ebx), %edi
- movl 4(%ebx), %esi
- movl 8(%ebx), %edx
+ movl %esi, %edx
+ movl efi32_boot_args+4(%ebp), %esi
movl $0x0, %ecx
1:
#endif
@@ -232,12 +231,16 @@ SYM_FUNC_END(startup_32)
.org 0x190
SYM_FUNC_START(efi32_stub_entry)
add $0x4, %esp /* Discard return address */
+ popl %ecx
+ popl %edx
+ popl %esi

call 1f
1: pop %ebp
subl $1b, %ebp

- movl %esp, efi32_boot_args(%ebp)
+ movl %ecx, efi32_boot_args(%ebp)
+ movl %edx, efi32_boot_args+4(%ebp)
sgdtl efi32_boot_gdt(%ebp)

/* Disable paging */
@@ -628,7 +631,7 @@ SYM_DATA_START_LOCAL(gdt)
SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end)

#ifdef CONFIG_EFI_MIXED
-SYM_DATA_LOCAL(efi32_boot_args, .long 0)
+SYM_DATA_LOCAL(efi32_boot_args, .long 0, 0)
#endif

/*
--
2.20.1
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