[PATCH 3/6] x86/entry_32: Add VERW just before userspace transition

[Pawan Gupta]

As done for entry_64, add support for executing VERW late in exit to
user path for 32-bit mode.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
---
 arch/x86/entry/entry_32.S | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 6e6af42e044a..bbf77d2aab2e 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -886,6 +886,9 @@ SYM_FUNC_START(entry_SYSENTER_32)
 	popfl
 	popl	%eax
 
+	/* Mitigate CPU data sampling attacks .e.g. MDS */
+	USER_CLEAR_CPU_BUFFERS
+
 	/*
 	 * Return back to the vDSO, which will pop ecx and edx.
 	 * Don't bother with DS and ES (they already contain __USER_DS).
@@ -954,6 +957,9 @@ restore_all_switch_stack:
 
 	/* Restore user state */
 	RESTORE_REGS pop=4			# skip orig_eax/error_code
+
+	/* Mitigate CPU data sampling attacks .e.g. MDS */
+	USER_CLEAR_CPU_BUFFERS
 .Lirq_return:
 	/*
 	 * ARCH_HAS_MEMBARRIER_SYNC_CORE rely on IRET core serialization
@@ -1146,6 +1152,8 @@ SYM_CODE_START(asm_exc_nmi)
 
 	/* Not on SYSENTER stack. */
 	call	exc_nmi
+	/* Mitigate CPU data sampling attacks .e.g. MDS */
+	USER_CLEAR_CPU_BUFFERS
 	jmp	.Lnmi_return
 
 .Lnmi_from_sysenter_stack:

-- 
2.34.1