[PATCH 21/28] efi/x86: preserve %ebx correctly in efi_set_virtual_address_map()

Ard Biesheuvel
2020-03-08T08:10:26Z

Commit 59f2a619a2db8611 ("efi: Add 'runtime' pointer to struct efi")
modified the assembler routine called by efi_set_virtual_address_map(),
to grab the 'runtime' EFI service pointer while running with paging
disabled (which is tricky to do in C code)

After the change, register %ebx is not restored correctly, resulting
in all kinds of weird behavior, so fix that.

Reported-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20200304133515.15035-1-ardb@kernel.org
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/x86/platform/efi/efi_stub_32.S | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/platform/efi/efi_stub_32.S b/arch/x86/platform/efi/efi_stub_32.S
index 09237236fb25..09ec84f6ef51 100644
--- a/arch/x86/platform/efi/efi_stub_32.S
+++ b/arch/x86/platform/efi/efi_stub_32.S
@@ -54,7 +54,7 @@ SYM_FUNC_START(efi_call_svam)
orl $0x80000000, %edx
movl %edx, %cr0

- pop %ebx
+ movl 16(%esp), %ebx
leave
ret
SYM_FUNC_END(efi_call_svam)
--
2.17.1