From: Ard Biesheuvel <ardb+git@google.com>
To: linux-kernel@vger.kernel.org
Cc: x86@kernel.org, Ard Biesheuvel <ardb@kernel.org>,
Arnd Bergmann <arnd@arndb.de>,
Eric Biederman <ebiederm@xmission.com>,
kexec@lists.infradead.org, Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Kees Cook <keescook@chromium.org>,
Bill Wendling <morbo@google.com>,
Justin Stitt <justinstitt@google.com>,
Masahiro Yamada <masahiroy@kernel.org>
Subject: [RFC PATCH 3/9] x86/purgatory: Drop pointless GDT switch
Date: Wed, 24 Apr 2024 17:53:13 +0200 [thread overview]
Message-ID: <20240424155309.1719454-14-ardb+git@google.com> (raw)
In-Reply-To: <20240424155309.1719454-11-ardb+git@google.com>
From: Ard Biesheuvel <ardb@kernel.org>
The x86 purgatory switches to a new GDT twice, and the first time, it
doesn't even bother to switch to the new code segment. Given that data
segment selectors are ignored in long mode, and the fact that the GDT is
reprogrammed again after returning from purgatory(), the first switch is
entirely pointless and can just be dropped altogether.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/x86/purgatory/setup-x86_64.S | 29 --------------------
1 file changed, 29 deletions(-)
diff --git a/arch/x86/purgatory/setup-x86_64.S b/arch/x86/purgatory/setup-x86_64.S
index 2d10ff88851d..f160fc729cbe 100644
--- a/arch/x86/purgatory/setup-x86_64.S
+++ b/arch/x86/purgatory/setup-x86_64.S
@@ -15,17 +15,6 @@
.code64
SYM_CODE_START(purgatory_start)
- /* Load a gdt so I know what the segment registers are */
- lgdt gdt(%rip)
-
- /* load the data segments */
- movl $0x18, %eax /* data segment */
- movl %eax, %ds
- movl %eax, %es
- movl %eax, %ss
- movl %eax, %fs
- movl %eax, %gs
-
/* Setup a stack */
leaq lstack_end(%rip), %rsp
@@ -34,24 +23,6 @@ SYM_CODE_START(purgatory_start)
jmp entry64
SYM_CODE_END(purgatory_start)
- .section ".rodata"
- .balign 16
-SYM_DATA_START_LOCAL(gdt)
- /* 0x00 unusable segment
- * 0x08 unused
- * so use them as the gdt ptr
- */
- .word gdt_end - gdt - 1
- .quad gdt
- .word 0, 0, 0
-
- /* 0x10 4GB flat code segment */
- .word 0xFFFF, 0x0000, 0x9A00, 0x00AF
-
- /* 0x18 4GB flat data segment */
- .word 0xFFFF, 0x0000, 0x9200, 0x00CF
-SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end)
-
.bss
.balign 16
SYM_DATA_START_LOCAL(lstack)
--
2.44.0.769.g3c40516874-goog
next prev parent reply other threads:[~2024-04-24 15:53 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-24 15:53 [RFC PATCH 0/9] kexec x86 purgatory cleanup Ard Biesheuvel
2024-04-24 15:53 ` [RFC PATCH 1/9] x86/purgatory: Drop function entry padding from purgatory Ard Biesheuvel
2024-04-24 15:53 ` [RFC PATCH 2/9] x86/purgatory: Simplify stack handling Ard Biesheuvel
2024-04-24 18:26 ` Nathan Chancellor
2024-04-26 21:32 ` Justin Stitt
2024-04-26 21:53 ` Nathan Chancellor
2024-04-26 22:01 ` Justin Stitt
2024-04-24 15:53 ` Ard Biesheuvel [this message]
2024-04-24 15:53 ` [RFC PATCH 4/9] x86/purgatory: Avoid absolute reference to GDT Ard Biesheuvel
2024-04-24 17:38 ` Brian Gerst
2024-04-24 17:53 ` Ard Biesheuvel
2024-04-24 19:00 ` Brian Gerst
2024-04-24 15:53 ` [RFC PATCH 5/9] x86/purgatory: Simplify GDT and drop data segment Ard Biesheuvel
2024-04-24 15:53 ` [RFC PATCH 6/9] kexec: Add support for fully linked purgatory executables Ard Biesheuvel
2024-04-24 15:53 ` [RFC PATCH 7/9] x86/purgatory: Use fully linked PIE ELF executable Ard Biesheuvel
2024-04-24 15:53 ` [RFC PATCH 8/9] x86/purgatory: Simplify references to regs array Ard Biesheuvel
2024-04-24 15:53 ` [RFC PATCH 9/9] kexec: Drop support for partially linked purgatory executables Ard Biesheuvel
2024-04-24 20:04 ` [RFC PATCH 0/9] kexec x86 purgatory cleanup Eric W. Biederman
2024-04-24 20:52 ` Ard Biesheuvel
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