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

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commit 48a2440d0f upstream.

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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Pawan Gupta 2024-09-25 15:25:44 -07:00 committed by Greg Kroah-Hartman
parent 0c6a7e2c60
commit 227358e897
1 changed files with 2 additions and 1 deletions
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3
arch/x86/entry/entry_32.S
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@ -1149,7 +1149,6 @@ SYM_CODE_START(asm_exc_nmi)
/* Not on SYSENTER stack. */ /* Not on SYSENTER stack. */
call exc_nmi call exc_nmi
CLEAR_CPU_BUFFERS
jmp .Lnmi_return jmp .Lnmi_return
.Lnmi_from_sysenter_stack: .Lnmi_from_sysenter_stack:
@ -1170,6 +1169,7 @@ SYM_CODE_START(asm_exc_nmi)
CHECK_AND_APPLY_ESPFIX CHECK_AND_APPLY_ESPFIX
RESTORE_ALL_NMI cr3_reg=%edi pop=4 RESTORE_ALL_NMI cr3_reg=%edi pop=4
CLEAR_CPU_BUFFERS
jmp .Lirq_return jmp .Lirq_return
#ifdef CONFIG_X86_ESPFIX32 #ifdef CONFIG_X86_ESPFIX32
@ -1211,6 +1211,7 @@ SYM_CODE_START(asm_exc_nmi)
* 1 - orig_ax * 1 - orig_ax
*/ */
lss (1+5+6)*4(%esp), %esp # back to espfix stack lss (1+5+6)*4(%esp), %esp # back to espfix stack
CLEAR_CPU_BUFFERS
jmp .Lirq_return jmp .Lirq_return
#endif #endif
SYM_CODE_END(asm_exc_nmi) SYM_CODE_END(asm_exc_nmi)