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

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>

diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index 2096ae09438e47276e8623e4002aa9200f6f8a66..1edf93e638975cdad5f42dc2cb113e894149c5bd 100644 (file)
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -476,7 +476,8 @@ 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;