Messages in this thread | | | Date | Tue, 15 Nov 2022 13:32:31 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v3 25/37] x86/shstk: Add user-mode shadow stack support |
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On Fri, Nov 04, 2022 at 03:35:52PM -0700, Rick Edgecombe wrote:
> +static int shstk_setup(void) > +{ > + struct thread_shstk *shstk = ¤t->thread.shstk; > + unsigned long addr, size; > + > + /* Already enabled */ > + if (features_enabled(CET_SHSTK)) > + return 0; > + > + /* Also not supported for 32 bit and x32 */ > + if (!cpu_feature_enabled(X86_FEATURE_USER_SHSTK) || in_32bit_syscall()) > + return -EOPNOTSUPP; > + > + size = adjust_shstk_size(0); > + addr = alloc_shstk(size); > + if (IS_ERR_VALUE(addr)) > + return PTR_ERR((void *)addr); > + > + fpregs_lock_and_load(); > + wrmsrl(MSR_IA32_PL3_SSP, addr + size); > + wrmsrl(MSR_IA32_U_CET, CET_SHSTK_EN);
This..
> + fpregs_unlock(); > + > + shstk->base = addr; > + shstk->size = size; > + features_set(CET_SHSTK); > + > + return 0; > +}
> +static int shstk_disable(void) > +{ > + if (!cpu_feature_enabled(X86_FEATURE_USER_SHSTK)) > + return -EOPNOTSUPP; > + > + /* Already disabled? */ > + if (!features_enabled(CET_SHSTK)) > + return 0; > + > + fpregs_lock_and_load(); > + /* Disable WRSS too when disabling shadow stack */ > + set_clr_bits_msrl(MSR_IA32_U_CET, 0, CET_SHSTK_EN);
And this... aren't very consistent in approach. Given there is no U_IBT yet, why complicate matters like this?
> + wrmsrl(MSR_IA32_PL3_SSP, 0); > + fpregs_unlock(); > + > + shstk_free(current); > + features_clr(CET_SHSTK); > + > + return 0; > +}
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