linux-kernel - [PATCH] x86/efistub: fix the missing KASLR_FLAG bit in boot

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Date: Tue, 26 Dec 2023 22:02:50 +0800
From: Yuntao Wang <ytcoode@...il.com>
To: linux-efi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Ard Biesheuvel <ardb@...nel.org>,
	"Borislav Petkov (AMD)" <bp@...en8.de>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Tom Lendacky <thomas.lendacky@....com>,
	Ingo Molnar <mingo@...nel.org>,
	Dionna Glaze <dionnaglaze@...gle.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	Yuntao Wang <ytcoode@...il.com>
Subject: [PATCH] x86/efistub: fix the missing KASLR_FLAG bit in boot_params->hdr.loadflags

When KASLR is enabled, the KASLR_FLAG bit in boot_params->hdr.loadflags
should be set to 1 to propagate KASLR status from compressed kernel to
kernel, just as the choose_random_location() function does.

Currently, when kernel is booted via efi stub, the KASLR_FLAG bit in
boot_params->hdr.loadflags is not set, even though it should be. This
causes some functions, such as kernel_randomize_memory(), not to execute
as expected. Fix it.

Signed-off-by: Yuntao Wang <ytcoode@...il.com>
---
 drivers/firmware/efi/libstub/x86-stub.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index da9b7b8d0716..b0c68593ad40 100644
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -787,7 +787,10 @@ static efi_status_t efi_decompress_kernel(unsigned long *kernel_entry)
 			efi_debug("AMI firmware v2.0 or older detected - disabling physical KASLR\n");
 			seed[0] = 0;
 		}
-	}
+
+		boot_params_ptr->hdr.loadflags |= KASLR_FLAG;
+	} else
+		boot_params_ptr->hdr.loadflags &= ~KASLR_FLAG;
 
 	status = efi_random_alloc(alloc_size, CONFIG_PHYSICAL_ALIGN, &addr,
 				  seed[0], EFI_LOADER_CODE,
-- 
2.43.0