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From: Ard Biesheuvel <ardb@kernel.org>
To: linux-efi@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>
Cc: Ard Biesheuvel <ardb@kernel.org>,
	linux-kernel@vger.kernel.org,
	Arvind Sankar <nivedita@alum.mit.edu>,
	Hans de Goede <hdegoede@redhat.com>
Subject: [PATCH 3/3] x86/efistub: disable paging at mixed mode entry
Date: Tue, 24 Dec 2019 14:29:09 +0100
Message-ID: <20191224132909.102540-4-ardb@kernel.org> (raw)
In-Reply-To: <20191224132909.102540-1-ardb@kernel.org>

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


  parent reply index

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-24 13:29 [GIT PULL 0/3] EFI fixes for v5.5 Ard Biesheuvel
2019-12-24 13:29 ` [PATCH 1/3] efi/earlycon: Fix write-combine mapping on x86 Ard Biesheuvel
2019-12-25 10:38   ` [tip: efi/urgent] " tip-bot2 for Arvind Sankar
2019-12-24 13:29 ` [PATCH 2/3] efi/libstub/random: Initialize pointer variables to zero for mixed mode Ard Biesheuvel
2019-12-25 10:38   ` [tip: efi/urgent] " tip-bot2 for Hans de Goede
2019-12-24 13:29 ` Ard Biesheuvel [this message]
2019-12-25 10:38   ` [tip: efi/urgent] x86/efistub: Disable paging at mixed mode entry tip-bot2 for Ard Biesheuvel
2019-12-25  9:50 ` [GIT PULL 0/3] EFI fixes for v5.5 Ingo Molnar

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