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From:   Rick Edgecombe <rick.p.edgecombe@intel.com>
To:     x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
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Cc:     rick.p.edgecombe@intel.com
Subject: [PATCH v2 33/39] x86/cpufeatures: Limit shadow stack to Intel CPUs
Date:   Thu, 29 Sep 2022 15:29:30 -0700
Message-Id: <20220929222936.14584-34-rick.p.edgecombe@intel.com>
In-Reply-To: <20220929222936.14584-1-rick.p.edgecombe@intel.com>
References: <20220929222936.14584-1-rick.p.edgecombe@intel.com>
Precedence: bulk

Shadow stack is supported on newer AMD processors, but the kernel
implementation has not been tested on them. Prevent basic issues from
showing up for normal users by disabling shadow stack on all CPUs except
Intel until it has been tested. At which point the limitation should be
removed.

Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>

---

v1:
 - New patch.

 arch/x86/kernel/cpu/common.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index d7415bb556b2..f7cacc5698d5 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -606,6 +606,14 @@ static __always_inline void setup_cet(struct cpuinfo_x86 *c)
 	if (!kernel_ibt && !user_shstk)
 		return;
 
+	/*
+	 * Shadow stack is supported on AMD processors, but has not been
+	 * tested. Only support it on Intel processors until this is done.
+	 * At which point, this vendor check should be removed.
+	 */
+	if (c->x86_vendor != X86_VENDOR_INTEL)
+		setup_clear_cpu_cap(X86_FEATURE_SHSTK);
+
 	if (kernel_ibt)
 		msr = CET_ENDBR_EN;
 
-- 
2.17.1