[PATCH AUTOSEL 4.9 6/9] x86/boot: Use unsigned comparison for addresses

[Sasha Levin]

From: Arvind Sankar <nivedita@xxxxxxxxxxxx>

[ Upstream commit 81a34892c2c7c809f9c4e22c5ac936ae673fb9a2 ]

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:

  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 the JAE instruction to perform a unsigned comparison instead, as physical
addresses should be considered unsigned.

Signed-off-by: Arvind Sankar <nivedita@xxxxxxxxxxxx>
Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20200301230436.2246909-6-nivedita@xxxxxxxxxxxx
Link: https://lore.kernel.org/r/20200308080859.21568-14-ardb@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 fd0b6a272dd5b..7532f6f536774 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -170,7 +170,7 @@ preferred_addr:
 	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 9e3a183561a9a..3fac2d133e4ec 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -104,7 +104,7 @@ ENTRY(startup_32)
 	notl	%eax
 	andl	%eax, %ebx
 	cmpl	$LOAD_PHYSICAL_ADDR, %ebx
-	jge	1f
+	jae	1f
 #endif
 	movl	$LOAD_PHYSICAL_ADDR, %ebx
 1:
@@ -339,7 +339,7 @@ preferred_addr:
 	notq	%rax
 	andq	%rax, %rbp
 	cmpq	$LOAD_PHYSICAL_ADDR, %rbp
-	jge	1f
+	jae	1f
 #endif
 	movq	$LOAD_PHYSICAL_ADDR, %rbp
 1:
-- 
2.20.1