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x86/entry_32: Clear CPU buffers after register restore in NMI return

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CPU buffers are currently cleared after call to exc_nmi, but before
register state is restored. This may be okay for MDS mitigation but not for
RDFS. Because RDFS mitigation requires CPU buffers to be cleared when
registers don't have any sensitive data.

Move CLEAR_CPU_BUFFERS after RESTORE_ALL_NMI.

Fixes: a0e2dab44d ("x86/entry_32: Add VERW just before userspace transition")
Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc:stable@vger.kernel.org
Link: https://lore.kernel.org/all/20240925-fix-dosemu-vm86-v7-2-1de0daca2d42%40linux.intel.com
This commit is contained in:
Pawan Gupta 2024-09-25 15:25:44 -07:00 committed by Dave Hansen
parent 2e2e5143d4
commit 48a2440d0f
1 changed files with 2 additions and 1 deletions
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3
arch/x86/entry/entry_32.S
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@ -1145,7 +1145,6 @@ SYM_CODE_START(asm_exc_nmi)
/* Not on SYSENTER stack. */
call exc_nmi
CLEAR_CPU_BUFFERS
jmp .Lnmi_return
.Lnmi_from_sysenter_stack:
@ -1166,6 +1165,7 @@ SYM_CODE_START(asm_exc_nmi)
CHECK_AND_APPLY_ESPFIX
RESTORE_ALL_NMI cr3_reg=%edi pop=4
CLEAR_CPU_BUFFERS
jmp .Lirq_return
#ifdef CONFIG_X86_ESPFIX32
@ -1207,6 +1207,7 @@ SYM_CODE_START(asm_exc_nmi)
* 1 - orig_ax
*/
lss (1+5+6)*4(%esp), %esp # back to espfix stack
CLEAR_CPU_BUFFERS
jmp .Lirq_return
#endif
SYM_CODE_END(asm_exc_nmi)