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

[Ard Biesheuvel]

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@xxxxxxxxxxxx>
Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20200304133515.15035-1-ardb@xxxxxxxxxx
Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
---
 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