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Subject[PATCH 13/28] x86/boot: Use unsigned comparison for addresses
Date
From: Arvind Sankar <nivedita@alum.mit.edu>

The load address is compared with LOAD_PHYSICAL_ADDR using a signed
comparison currently (using jge instruction).

When loading a 64-bit kernel using the new efi32_pe_entry point added by
commit 97aa276579b2 ("efi/x86: Add true mixed mode entry point into
.compat section") using qemu with -m 3072, the firmware actually loads
us above 2Gb, resulting in a very early crash.

Use jae instruction to perform unsigned comparison instead, as physical
addresses should be considered as unsigned.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200301230436.2246909-6-nivedita@alum.mit.edu
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/x86/boot/compressed/head_32.S | 2 +-
arch/x86/boot/compressed/head_64.S | 4 ++--
2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index 9ffc9454fd22..f250fc49cd61 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -105,7 +105,7 @@ SYM_FUNC_START(startup_32)
notl %eax
andl %eax, %ebx
cmpl $LOAD_PHYSICAL_ADDR, %ebx
- jge 1f
+ jae 1f
#endif
movl $LOAD_PHYSICAL_ADDR, %ebx
1:
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 08351d16ccc0..1199c4ef0c83 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -105,7 +105,7 @@ SYM_FUNC_START(startup_32)
notl %eax
andl %eax, %ebx
cmpl $LOAD_PHYSICAL_ADDR, %ebx
- jge 1f
+ jae 1f
#endif
movl $LOAD_PHYSICAL_ADDR, %ebx
1:
@@ -305,7 +305,7 @@ SYM_CODE_START(startup_64)
notq %rax
andq %rax, %rbp
cmpq $LOAD_PHYSICAL_ADDR, %rbp
- jge 1f
+ jae 1f
#endif
movq $LOAD_PHYSICAL_ADDR, %rbp
1:
--
2.17.1
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