6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
commit 48a2440d0f20c826b884e04377ccc1e4696c84e9 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: a0e2dab44d22 ("x86/entry_32: Add VERW just before userspace transition")
Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc:stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/all/20240925-fix-dosemu-vm86-v7-2-1de0daca2d42%40linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/entry/entry_32.S | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -1149,7 +1149,6 @@ SYM_CODE_START(asm_exc_nmi)
/* Not on SYSENTER stack. */
call exc_nmi
- CLEAR_CPU_BUFFERS
jmp .Lnmi_return
.Lnmi_from_sysenter_stack:
@@ -1170,6 +1169,7 @@ 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
@@ -1211,6 +1211,7 @@ 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)
