x86/efistub: Don't clear BSS twice in mixed mode

[ Upstream commit df7ecce842b846a04d087ba85fdb79a90e26a1b0 ]

Clearing BSS should only be done once, at the very beginning.
efi_pe_entry() is the entrypoint from the firmware, which may not clear
BSS and so it is done explicitly. However, efi_pe_entry() is also used
as an entrypoint by the mixed mode startup code, in which case BSS will
already have been cleared, and doing it again at this point will corrupt
global variables holding the firmware's GDT/IDT and segment selectors.

So make the memset() conditional on whether the EFI stub is running in
native mode.

Fixes: b3810c5a2cc4a666 ("x86/efistub: Clear decompressor BSS in native EFI entrypoint")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index 681f576ec02a00263c8d4061d670af6fe8f180ba..c9857ee3880c240fc4c6675613f8fcd014796e9b 100644 (file)
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -467,7 +467,8 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
        efi_status_t status;
        char *cmdline_ptr;
 
-       memset(_bss, 0, _ebss - _bss);
+       if (efi_is_native())
+               memset(_bss, 0, _ebss - _bss);
 
        efi_system_table = sys_table_arg;