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From: Arvind Sankar <nivedita@alum.mit.edu>
To: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Ard Biesheuvel <ardb@kernel.org>
Cc: linux-efi@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v2 3/7] x86/boot: Reload GDTR after copying to the end of the buffer
Date: Sun,  2 Feb 2020 12:13:49 -0500
Message-ID: <20200202171353.3736319-4-nivedita@alum.mit.edu> (raw)
In-Reply-To: <20200202171353.3736319-1-nivedita@alum.mit.edu>

The GDT may get overwritten during the copy or during extract_kernel,
which will cause problems if any segment register is touched before the
GDTR is reloaded by the decompressed kernel. For safety update the GDTR
to point to the GDT within the copied kernel.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
---
 arch/x86/boot/compressed/head_64.S | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index c56b30bd9c7b..27eb2a6786db 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -439,6 +439,16 @@ trampoline_return:
 	cld
 	popq	%rsi
 
+	/*
+	 * The GDT may get overwritten either during the copy we just did or
+	 * during extract_kernel below. To avoid any issues, repoint the GDTR
+	 * to the new copy of the GDT.
+	 */
+	leaq	gdt64(%rbx), %rax
+	subq	%rbp, 2(%rax)
+	addq	%rbx, 2(%rax)
+	lgdt	(%rax)
+
 /*
  * Jump to the relocated address.
  */
-- 
2.24.1


  parent reply index

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-30 20:04 [PATCH 0/8] Remove 64-bit GDT setup in efi_main + doc fixes Arvind Sankar
2020-01-30 20:04 ` [PATCH 1/8] efi/x86: Use C wrapper instead of inline assembly Arvind Sankar
2020-01-30 20:04 ` [PATCH 2/8] efi/x86: Allocate the GDT pointer on the stack Arvind Sankar
2020-01-30 20:04 ` [PATCH 3/8] efi/x86: Factor GDT setup code into a function Arvind Sankar
2020-01-30 20:04 ` [PATCH 4/8] efi/x86: Only setup the GDT for 32-bit kernel Arvind Sankar
2020-01-30 20:04 ` [PATCH 5/8] efi/x86: Allocate only the required 32 bytes for the GDT Arvind Sankar
2020-01-30 20:04 ` [PATCH 6/8] efi/x86: Change __KERNEL_{CS,DS} to __BOOT_{CS,DS} Arvind Sankar
2020-01-30 20:04 ` [PATCH 7/8] Documentation/x86/boot: Clarify segment requirements for EFI handover Arvind Sankar
2020-01-31 19:24   ` Arvind Sankar
2020-01-30 20:04 ` [PATCH 8/8] Documentation/x86/boot: Correct segment requirements for 64-bit boot Arvind Sankar
2020-01-31  8:42 ` [PATCH 0/8] Remove 64-bit GDT setup in efi_main + doc fixes Ard Biesheuvel
2020-01-31  9:31   ` Ard Biesheuvel
2020-01-31 19:10     ` Arvind Sankar
2020-02-02 17:13 ` [PATCH v2 0/7] x86/efi,boot: GDT handling cleanup/fixes Arvind Sankar
2020-02-02 17:13   ` [PATCH v2 1/7] x86/boot: Remove KEEP_SEGMENTS support Arvind Sankar
2020-02-02 17:13   ` [PATCH v2 2/7] efi/x86: Don't depend on firmware GDT layout Arvind Sankar
2020-02-02 17:54     ` Ard Biesheuvel
2020-02-02 18:18       ` Arvind Sankar
2020-02-02 17:13   ` Arvind Sankar [this message]
2020-02-02 17:13   ` [PATCH v2 4/7] x86/boot: Clear direction and interrupt flags in startup_64 Arvind Sankar
2020-02-02 17:13   ` [PATCH v2 5/7] efi/x86: Remove GDT setup from efi_main Arvind Sankar
2020-02-02 17:13   ` [PATCH v2 6/7] x86/boot: GDT limit value should be size - 1 Arvind Sankar
2020-02-02 17:13   ` [PATCH v2 7/7] x86/boot: Micro-optimize GDT loading instructions Arvind Sankar
2020-02-02 18:01   ` [PATCH v2 0/7] x86/efi,boot: GDT handling cleanup/fixes Ard Biesheuvel

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