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Date: Tue, 20 Jul 2021 10:13:43 -0700 From: "Yu, Yu-cheng" <yu-cheng.yu@...el.com> To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>, "Xu, Pengfei" <pengfei.xu@...el.com>, "vedvyas.shanbhogue@...el.com" <vedvyas.shanbhogue@...el.com>, "tglx@...utronix.de" <tglx@...utronix.de>, "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>, "Lutomirski, Andy" <luto@...nel.org>, "nadav.amit@...il.com" <nadav.amit@...il.com>, "peterz@...radead.org" <peterz@...radead.org>, "corbet@....net" <corbet@....net>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "jannh@...gle.com" <jannh@...gle.com>, "x86@...nel.org" <x86@...nel.org>, "bp@...en8.de" <bp@...en8.de>, "pavel@....cz" <pavel@....cz>, "rdunlap@...radead.org" <rdunlap@...radead.org>, "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>, "Dave.Martin@....com" <Dave.Martin@....com>, "arnd@...db.de" <arnd@...db.de>, "bsingharora@...il.com" <bsingharora@...il.com>, "mike.kravetz@...cle.com" <mike.kravetz@...cle.com>, "oleg@...hat.com" <oleg@...hat.com>, "fweimer@...hat.com" <fweimer@...hat.com>, "keescook@...omium.org" <keescook@...omium.org>, "gorcunov@...il.com" <gorcunov@...il.com>, "Huang, Haitao" <haitao.huang@...el.com>, "hpa@...or.com" <hpa@...or.com>, "mingo@...hat.com" <mingo@...hat.com>, "Shankar, Ravi V" <ravi.v.shankar@...el.com>, "hjl.tools@...il.com" <hjl.tools@...il.com>, "linux-mm@...ck.org" <linux-mm@...ck.org>, "esyr@...hat.com" <esyr@...hat.com>, "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>, "Yang, Weijiang" <weijiang.yang@...el.com>, "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com> Subject: Re: [PATCH v27 23/31] x86/cet/shstk: Add user-mode shadow stack support 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 <yu-cheng.yu@...el.com> >> Cc: Kees Cook <keescook@...omium.org> [...] >> 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) >> +{ >> + struct thread_shstk *shstk = ¤t->thread.shstk; >> + unsigned long addr, size; >> + >> + if (!cpu_feature_enabled(X86_FEATURE_SHSTK)) >> + return -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. > Indeed that is the case. We can simply remove the test of X86_FEATURE_SHSTK. Thanks, Yu-cheng
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