The following commit has been merged into the x86/urgent branch of tip:

Commit-ID: 48a2440d0f20c826b884e04377ccc1e4696c84e9 Gitweb: https://git.kernel.org/tip/48a2440d0f20c826b884e04377ccc1e4696c84e9 Author: Pawan Gupta pawan.kumar.gupta@linux.intel.com AuthorDate: Wed, 25 Sep 2024 15:25:44 -07:00 Committer: Dave Hansen dave.hansen@linux.intel.com CommitterDate: Tue, 08 Oct 2024 15:16:28 -07:00

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

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@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%40lin... --- arch/x86/entry/entry_32.S | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index 9ad6cd8..20be575 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -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)