Commit 81a34892 authored Mar 08, 2020 by Arvind Sankar Committed by Ingo Molnar Mar 08, 2020

x86/boot: Use unsigned comparison for addresses



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:

  97aa2765 ("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@alum.mit.edu>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200301230436.2246909-6-nivedita@alum.mit.edu
Link: https://lore.kernel.org/r/20200308080859.21568-14-ardb@kernel.org

parent 8acf63ef

arch/x86/boot/compressed/head_32.S

+1 −1

Original line number	Diff line number	Diff line
		@@ -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:

arch/x86/boot/compressed/head_64.S

+2 −2

Original line number	Diff line number	Diff line
		@@ -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:

Admin message