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From:   Kees Cook <keescook@chromium.org>
To:     linux-kernel@vger.kernel.org
Cc:     Kees Cook <keescook@chromium.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        kvm@vger.kernel.org, "Gustavo A. R. Silva" <gustavoars@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
        dri-devel@lists.freedesktop.org, linux-staging@lists.linux.dev,
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        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        linux-hardening@vger.kernel.org
Subject: [PATCH v2 53/63] KVM: x86: Use struct_group() to zero decode cache
Date:   Tue, 17 Aug 2021 23:05:23 -0700
Message-Id: <20210818060533.3569517-54-keescook@chromium.org>
In-Reply-To: <20210818060533.3569517-1-keescook@chromium.org>
References: <20210818060533.3569517-1-keescook@chromium.org>
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In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring fields.

Add struct_group() to mark region of struct x86_emulate_ctxt that should
be initialized to zero.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Jim Mattson <jmattson@google.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: x86@kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: kvm@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 arch/x86/kvm/emulate.c     |  3 +--
 arch/x86/kvm/kvm_emulate.h | 19 +++++++++++--------
 2 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 2837110e66ed..2608a047e769 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -5377,8 +5377,7 @@ static int fastop(struct x86_emulate_ctxt *ctxt, fastop_t fop)
 
 void init_decode_cache(struct x86_emulate_ctxt *ctxt)
 {
-	memset(&ctxt->rip_relative, 0,
-	       (void *)&ctxt->modrm - (void *)&ctxt->rip_relative);
+	memset(&ctxt->decode_cache, 0, sizeof(ctxt->decode_cache));
 
 	ctxt->io_read.pos = 0;
 	ctxt->io_read.end = 0;
diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h
index 68b420289d7e..9b8afcb8ad39 100644
--- a/arch/x86/kvm/kvm_emulate.h
+++ b/arch/x86/kvm/kvm_emulate.h
@@ -341,14 +341,17 @@ struct x86_emulate_ctxt {
 	 * the rest are initialized unconditionally in x86_decode_insn
 	 * or elsewhere
 	 */
-	bool rip_relative;
-	u8 rex_prefix;
-	u8 lock_prefix;
-	u8 rep_prefix;
-	/* bitmaps of registers in _regs[] that can be read */
-	u32 regs_valid;
-	/* bitmaps of registers in _regs[] that have been written */
-	u32 regs_dirty;
+	struct_group(decode_cache,
+		bool rip_relative;
+		u8 rex_prefix;
+		u8 lock_prefix;
+		u8 rep_prefix;
+		/* bitmaps of registers in _regs[] that can be read */
+		u32 regs_valid;
+		/* bitmaps of registers in _regs[] that have been written */
+		u32 regs_dirty;
+	);
+
 	/* modrm */
 	u8 modrm;
 	u8 modrm_mod;
-- 
2.30.2