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

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Message-ID: <20231020-delay-verw-v1-3-cff54096326d@linux.intel.com>
Date:   Fri, 20 Oct 2023 13:45:09 -0700
From:   Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>, tony.luck@...el.com,
        ak@...ux.intel.com, tim.c.chen@...ux.intel.com
Cc:     linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        kvm@...r.kernel.org,
        Alyssa Milburn <alyssa.milburn@...ux.intel.com>,
        Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
        antonio.gomez.iglesias@...ux.intel.com,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Subject: [PATCH  3/6] x86/entry_32: Add VERW just before userspace transition

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@...ux.intel.com>
---
 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