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x86/entry: Remove UNTRAIN_RET from native_irq_return_ldt 

UNTRAIN_RET is not needed in native_irq_return_ldt because RET
untraining has already been done at this point.

In addition, when the RETBleed mitigation is IBPB, UNTRAIN_RET clobbers
several registers (AX, CX, DX) so here it trashes user values which are
in these registers.

Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/35b0d50f-12d1-10c3-f5e8-d6c140486d4a@oracle.com
This commit is contained in:
Alexandre Chartre 2022-07-13 21:58:08 +02:00 committed by Borislav Petkov
parent 33a8573bdf
commit d16e0b2667
1 changed files with 0 additions and 1 deletions
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arch/x86/entry/entry_64.S
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@ -727,7 +727,6 @@ native_irq_return_ldt:
pushq %rdi /* Stash user RDI */
swapgs /* to kernel GS */
SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi /* to kernel CR3 */
UNTRAIN_RET
movq PER_CPU_VAR(espfix_waddr), %rdi
movq %rax, (0*8)(%rdi) /* user RAX */