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Tue, 20 Jul 2021 17:13:51 +0000 Subject: Re: [PATCH v27 23/31] x86/cet/shstk: Add user-mode shadow stack support To: "Edgecombe, Rick P" , "Xu, Pengfei" , "vedvyas.shanbhogue@intel.com" , "tglx@linutronix.de" , "linux-arch@vger.kernel.org" , "Lutomirski, Andy" , "nadav.amit@gmail.com" , "peterz@infradead.org" , "corbet@lwn.net" , "linux-kernel@vger.kernel.org" , "jannh@google.com" , "x86@kernel.org" , "bp@alien8.de" , "pavel@ucw.cz" , "rdunlap@infradead.org" , "linux-api@vger.kernel.org" , "Dave.Martin@arm.com" , "arnd@arndb.de" , "bsingharora@gmail.com" , "mike.kravetz@oracle.com" , "oleg@redhat.com" , "fweimer@redhat.com" , "keescook@chromium.org" , "gorcunov@gmail.com" , "Huang, Haitao" , "hpa@zytor.com" , "mingo@redhat.com" , "Shankar, Ravi V" , "hjl.tools@gmail.com" , "linux-mm@kvack.org" , "esyr@redhat.com" , "linux-doc@vger.kernel.org" , "Yang, Weijiang" , "dave.hansen@linux.intel.com" References: <20210521221211.29077-1-yu-cheng.yu@intel.com> <20210521221211.29077-24-yu-cheng.yu@intel.com> <798a369d3e7339a42f390321b56423cafd4e477f.camel@intel.com> From: "Yu, Yu-cheng" Message-ID: <44269526-6b77-f300-90cf-5501feac426c@intel.com> Date: Tue, 20 Jul 2021 10:13:43 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; 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dkim=pass header.d=intel.onmicrosoft.com header.s=selector2-intel-onmicrosoft-com header.b=m4Kl34IC; spf=none (imf27.hostedemail.com: domain of yu-cheng.yu@intel.com has no SPF policy when checking 192.55.52.93) smtp.mailfrom=yu-cheng.yu@intel.com; dmarc=fail reason="No valid SPF, DKIM not aligned (relaxed)" header.from=intel.com (policy=none) X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 774FC70009D0 X-Stat-Signature: kixcams8xpsouyo7yjtqusbi3bi9dwxq X-HE-Tag: 1626801406-202877 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 7/19/2021 11:23 AM, Edgecombe, Rick P wrote: > On Fri, 2021-05-21 at 15:12 -0700, Yu-cheng Yu wrote: >> Introduce basic shadow stack enabling/disabling/allocation routines. >> A task's shadow stack is allocated from memory with VM_SHADOW_STACK >> flag >> and has a fixed size of min(RLIMIT_STACK, 4GB). >> >> Signed-off-by: Yu-cheng Yu >> Cc: Kees Cook [...] >> diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c >> new file mode 100644 >> index 000000000000..5ea2b494e9f9 >> --- /dev/null >> +++ b/arch/x86/kernel/shstk.c [...] >> +int shstk_setup(void) >> +{ >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0struct thread_shstk *shstk = =3D ¤t->thread.shstk; >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0unsigned long addr, size; >> + >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if (!cpu_feature_enabled(X8= 6_FEATURE_SHSTK)) >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0return -EOPNOTSUPP; > The only caller of this will skip it if > !cpu_feature_enabled(X86_FEATURE_SHSTK), so this is dead logic. Same > pattern in the IBT patch. >=20 Indeed that is the case. We can simply remove the test of=20 X86_FEATURE_SHSTK. Thanks, Yu-cheng