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From: Arvind Sankar <nivedita@alum.mit.edu>
To: Ingo Molnar <mingo@kernel.org>
Cc: Ard Biesheuvel <ardb@kernel.org>,
	linux-efi@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v2 1/1] x86/boot/compressed: Fix reloading of GDTR post-relocation
Date: Wed, 26 Feb 2020 18:00:31 -0500	[thread overview]
Message-ID: <20200226230031.3011645-2-nivedita@alum.mit.edu> (raw)
In-Reply-To: <20200226204515.2752095-1-nivedita@alum.mit.edu>

Commit ef5a7b5eb13e ("efi/x86: Remove GDT setup from efi_main")
introduced GDT setup into the 32-bit kernel's startup_32, and reloads
the GDTR after relocating the kernel for paranoia's sake.

Commit 32d009137a56 ("x86/boot: Reload GDTR after copying to the end of
the buffer") introduced a similar GDTR reload in the 64-bit kernel.

The GDTR is adjusted by init_size - _end, however this may not be the
correct offset to apply if the kernel was loaded at a misaligned address
or below LOAD_PHYSICAL_ADDR, as in that case the decompression buffer
has an additional offset from the original load address.

This should never happen for a conformant bootloader, but we're being
paranoid anyway, so just store the new GDT address in there instead of
adding any offsets, which is simpler as well.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Fixes: ef5a7b5eb13e ("efi/x86: Remove GDT setup from efi_main")
Fixes: 32d009137a56 ("x86/boot: Reload GDTR after copying to the end of the buffer")
---
 arch/x86/boot/compressed/head_32.S | 9 ++++-----
 arch/x86/boot/compressed/head_64.S | 4 ++--
 2 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index 356060c5332c..2f8138b71ea9 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -139,12 +139,11 @@ SYM_FUNC_START(startup_32)
 	/*
 	 * 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. EAX still contains the previously
-	 * calculated relocation offset of init_size - _end.
+	 * to the new copy of the GDT.
 	 */
-	leal	gdt(%ebx), %edx
-	addl	%eax, 2(%edx)
-	lgdt	(%edx)
+	leal	gdt(%ebx), %eax
+	movl	%eax, 2(%eax)
+	lgdt	(%eax)
 
 /*
  * Jump to the relocated address.
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index f7bacc4c1494..fcf8feaa57ea 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -456,8 +456,8 @@ trampoline_return:
 	 * to the new copy of the GDT.
 	 */
 	leaq	gdt64(%rbx), %rax
-	subq	%rbp, 2(%rax)
-	addq	%rbx, 2(%rax)
+	leaq	gdt(%rbx), %rdx
+	movq	%rdx, 2(%rax)
 	lgdt	(%rax)
 
 /*
-- 
2.24.1


  parent reply	other threads:[~2020-02-26 23:00 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-24 13:38 [GIT PULL v2] EFI updates for v5.7 Ard Biesheuvel
2020-02-26 14:27 ` Ingo Molnar
2020-02-26 14:50   ` Ard Biesheuvel
2020-02-26 20:45   ` [PATCH 0/1] Small fix to boot-time GDT handling Arvind Sankar
2020-02-26 23:00     ` [PATCH v2 " Arvind Sankar
2020-02-26 23:00     ` Arvind Sankar [this message]
2020-02-27  8:12       ` [PATCH v2 1/1] x86/boot/compressed: Fix reloading of GDTR post-relocation Ingo Molnar
2020-02-27 15:16         ` Arvind Sankar
2020-02-27 15:21           ` Ard Biesheuvel
2020-02-27 15:54             ` Arvind Sankar
2020-02-27 17:47               ` Ard Biesheuvel
2020-02-27 18:03                 ` Arvind Sankar
2020-02-29  9:24                   ` Ingo Molnar
2020-02-29 16:50                     ` Arvind Sankar
2020-02-26 20:45   ` [PATCH 1/1] x86/boot/compressed/32: " Arvind Sankar

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