Messages in this thread | | | Date | Thu, 26 Aug 2021 18:25:17 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v29 23/32] x86/cet/shstk: Add user-mode shadow stack support |
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On Fri, Aug 20, 2021 at 11:11:52AM -0700, Yu-cheng Yu wrote: > diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h > new file mode 100644 > index 000000000000..6432baf4de1f > --- /dev/null > +++ b/arch/x86/include/asm/cet.h > @@ -0,0 +1,30 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +#ifndef _ASM_X86_CET_H > +#define _ASM_X86_CET_H > + > +#ifndef __ASSEMBLY__ > +#include <linux/types.h> > + > +struct task_struct; > + > +/* > + * Per-thread CET status > + */
That comment is superfluous and wrong now. The struct name says exactly what that thing is.
> +static unsigned long alloc_shstk(unsigned long size) > +{ > + int flags = MAP_ANONYMOUS | MAP_PRIVATE; > + struct mm_struct *mm = current->mm; > + unsigned long addr, populate;
s/populate/unused/
> + > + mmap_write_lock(mm); > + addr = do_mmap(NULL, 0, size, PROT_READ, flags, VM_SHADOW_STACK, 0, > + &populate, NULL); > + mmap_write_unlock(mm); > + > + return addr; > +} > + > +int shstk_setup(void) > +{ > + struct thread_shstk *shstk = ¤t->thread.shstk; > + unsigned long addr, size; > + int err; > + > + if (!cpu_feature_enabled(X86_FEATURE_SHSTK)) > + return 0; > + > + size = round_up(min_t(unsigned long long, rlimit(RLIMIT_STACK), SZ_4G), PAGE_SIZE); > + addr = alloc_shstk(size); > + if (IS_ERR_VALUE(addr)) > + return PTR_ERR((void *)addr); > + > + start_update_msrs();
You're setting CET_U with the MSR writes below. Why do you need to do XRSTOR here? To zero out PL[012]_SSP?
If so, you can WRMSR those too - no need for a full XRSTOR...
> + err = wrmsrl_safe(MSR_IA32_PL3_SSP, addr + size); > + if (!err) > + wrmsrl_safe(MSR_IA32_U_CET, CET_SHSTK_EN); > + end_update_msrs(); > + > + if (!err) { > + shstk->base = addr; > + shstk->size = size; > + } > + > + return err; > +}
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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