mirrors/linux
1
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2026-05-05 01:32:47 -04:00
Code Issues Packages Projects Releases Wiki Activity

x86/startup_64: Drop long return to initial_code pointer

Browse Source 
Since

  866b556efa ("x86/head/64: Install startup GDT")

the primary startup sequence sets the code segment register (CS) to
__KERNEL_CS before calling into the startup code shared between primary
and secondary boot.

This means a simple indirect call is sufficient here.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240129180502.4069817-24-ardb+git@google.com
This commit is contained in:
Ard Biesheuvel
2024-01-29 19:05:06 +01:00
committed by Borislav Petkov (AMD)
parent 41bccc98fb
commit 1567570624
1 changed files with 3 additions and 32 deletions
Download Patch File Download Diff File Expand all files Collapse all files

35
arch/x86/kernel/head_64.S
View File

@@ -428,39 +428,10 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
movq %r15, %rdi
.Ljump_to_C_code:
/*
* Jump to run C code and to be on a real kernel address.
* Since we are running on identity-mapped space we have to jump
* to the full 64bit address, this is only possible as indirect
* jump. In addition we need to ensure %cs is set so we make this
* a far return.
*
* Note: do not change to far jump indirect with 64bit offset.
*
* AMD does not support far jump indirect with 64bit offset.
* AMD64 Architecture Programmer's Manual, Volume 3: states only
* JMP FAR mem16:16 FF /5 Far jump indirect,
* with the target specified by a far pointer in memory.
* JMP FAR mem16:32 FF /5 Far jump indirect,
* with the target specified by a far pointer in memory.
*
* Intel64 does support 64bit offset.
* Software Developer Manual Vol 2: states:
* FF /5 JMP m16:16 Jump far, absolute indirect,
* address given in m16:16
* FF /5 JMP m16:32 Jump far, absolute indirect,
* address given in m16:32.
* REX.W + FF /5 JMP m16:64 Jump far, absolute indirect,
* address given in m16:64.
*/
pushq $.Lafter_lret # put return address on stack for unwinder
xorl %ebp, %ebp # clear frame pointer
movq initial_code(%rip), %rax
pushq $__KERNEL_CS # set correct cs
pushq %rax # target address in negative space
lretq
.Lafter_lret:
ANNOTATE_NOENDBR
ANNOTATE_RETPOLINE_SAFE
callq *initial_code(%rip)
ud2
SYM_CODE_END(secondary_startup_64)
#include "verify_cpu.S"