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Shutemov" To: Yu-cheng Yu Cc: x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin , Weijiang Yang , Pengfei Xu , Haitao Huang , "Kirill A . Shutemov" Subject: Re: [PATCH v24 14/30] x86/mm: Shadow Stack page fault error checking Message-ID: <20210409151224.4tlklypbjpxcztpt@box.shutemov.name> References: <20210401221104.31584-1-yu-cheng.yu@intel.com> <20210401221104.31584-15-yu-cheng.yu@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210401221104.31584-15-yu-cheng.yu@intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Thu, Apr 01, 2021 at 03:10:48PM -0700, Yu-cheng Yu wrote: > Shadow stack accesses are those that are performed by the CPU where it > expects to encounter a shadow stack mapping. These accesses are performed > implicitly by CALL/RET at the site of the shadow stack pointer. These > accesses are made explicitly by shadow stack management instructions like > WRUSSQ. > > Shadow stacks accesses to shadow-stack mapping can see faults in normal, > valid operation just like regular accesses to regular mappings. Shadow > stacks need some of the same features like delayed allocation, swap and > copy-on-write. > > Shadow stack accesses can also result in errors, such as when a shadow > stack overflows, or if a shadow stack access occurs to a non-shadow-stack > mapping. > > In handling a shadow stack page fault, verify it occurs within a shadow > stack mapping. It is always an error otherwise. For valid shadow stack > accesses, set FAULT_FLAG_WRITE to effect copy-on-write. Because clearing > _PAGE_DIRTY (vs. _PAGE_RW) is used to trigger the fault, shadow stack read > fault and shadow stack write fault are not differentiated and both are > handled as a write access. > > Signed-off-by: Yu-cheng Yu > Reviewed-by: Kees Cook Reviewed-by: Kirill A. Shutemov -- Kirill A. Shutemov