linux-kernel - [PATCH 6.1 450/451] x86/efistub: Don't clear BSS twice in mixed mode

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Date: Sun, 24 Mar 2024 19:12:06 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Ard Biesheuvel <ardb@...nel.org>,
	Sasha Levin <sashal@...nel.org>
Subject: [PATCH 6.1 450/451] x86/efistub: Don't clear BSS twice in mixed mode

From: Ard Biesheuvel <ardb@...nel.org>

[ 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@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/firmware/efi/libstub/x86-stub.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index aa07051459f52..dc50dda40239e 100644
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -434,7 +434,8 @@ 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;

-- 
2.43.0