linux-kernel - [PATCH v2 33/39] x86/cpufeatures: Limit shadow stack to Intel CPUs

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Date:   Thu, 29 Sep 2022 15:29:30 -0700
From:   Rick Edgecombe <rick.p.edgecombe@...el.com>
To:     x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H . J . Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V . Shankar" <ravi.v.shankar@...el.com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        joao.moreira@...el.com, John Allen <john.allen@....com>,
        kcc@...gle.com, eranian@...gle.com, rppt@...nel.org,
        jamorris@...ux.microsoft.com, dethoma@...rosoft.com
Cc:     rick.p.edgecombe@...el.com
Subject: [PATCH v2 33/39] x86/cpufeatures: Limit shadow stack to Intel CPUs

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@...el.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