From: Ard Biesheuvel <ardb@kernel.org>
To: linux-efi@vger.kernel.org
Cc: hdegoede@redhat.com, x86@kernel.org, nivedita@alum.mit.edu,
Ard Biesheuvel <ardb@kernel.org>
Subject: [PATCH] x86/efistub: disable paging at mixed mode entry
Date: Mon, 23 Dec 2019 16:21:57 +0100 [thread overview]
Message-ID: <20191223152157.68545-1-ardb@kernel.org> (raw)
The EFI mixed mode entry code goes through the ordinary startup_32()
routine before jumping into the kernel's EFI boot code in 64-bit
mode. The 32-bit startup code must be entered with paging disabled,
but this is not documented as a requirement for the EFI handover
protocol, and so we should disable paging explicitly when entering
the kernel from 32-bit EFI firmware.
Cc: <stable@vger.kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/x86/boot/compressed/head_64.S | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 58a512e33d8d..ee60b81944a7 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -244,6 +244,11 @@ SYM_FUNC_START(efi32_stub_entry)
leal efi32_config(%ebp), %eax
movl %eax, efi_config(%ebp)
+ /* Disable paging */
+ movl %cr0, %eax
+ btrl $X86_CR0_PG_BIT, %eax
+ movl %eax, %cr0
+
jmp startup_32
SYM_FUNC_END(efi32_stub_entry)
#endif
--
2.20.1
next reply other threads:[~2019-12-23 15:23 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-23 15:21 Ard Biesheuvel [this message]
2019-12-24 2:15 ` [PATCH] x86/efistub: disable paging at mixed mode entry Andy Lutomirski
2019-12-24 7:38 ` Ard Biesheuvel
2019-12-24 7:47 ` Andy Lutomirski
2019-12-24 7:50 ` Ard Biesheuvel
2019-12-24 9:29 ` Andy Lutomirski
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