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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 17/30] mm: Add guard pages around a shadow stack. Message-ID: <20210409152254.tmpfubsksrd2qbeq@box.shutemov.name> References: <20210401221104.31584-1-yu-cheng.yu@intel.com> <20210401221104.31584-18-yu-cheng.yu@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210401221104.31584-18-yu-cheng.yu@intel.com> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: B23DAA000140 X-Stat-Signature: egsb9ju4q61x9pkdpc9cpewibxjq7csd Received-SPF: none (shutemov.name>: No applicable sender policy available) receiver=imf07; identity=mailfrom; envelope-from=""; helo=mail-lj1-f171.google.com; client-ip=209.85.208.171 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617981776-991649 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 Thu, Apr 01, 2021 at 03:10:51PM -0700, Yu-cheng Yu wrote: > INCSSP(Q/D) increments shadow stack pointer and 'pops and discards' the > first and the last elements in the range, effectively touches those memory > areas. > > The maximum moving distance by INCSSPQ is 255 * 8 = 2040 bytes and > 255 * 4 = 1020 bytes by INCSSPD. Both ranges are far from PAGE_SIZE. > Thus, putting a gap page on both ends of a shadow stack prevents INCSSP, > CALL, and RET from going beyond. > > Signed-off-by: Yu-cheng Yu > Cc: Kees Cook > Cc: Kirill A. Shutemov > --- > v24: > - Instead changing vm_*_gap(), create x86-specific versions. > > arch/x86/include/asm/page_types.h | 17 +++++++++++++++ > arch/x86/mm/mmap.c | 36 +++++++++++++++++++++++++++++++ > include/linux/mm.h | 4 ++++ > 3 files changed, 57 insertions(+) > > diff --git a/arch/x86/include/asm/page_types.h b/arch/x86/include/asm/page_types.h > index a506a411474d..3a5529bcfd76 100644 > --- a/arch/x86/include/asm/page_types.h > +++ b/arch/x86/include/asm/page_types.h > @@ -73,6 +73,23 @@ bool pfn_range_is_mapped(unsigned long start_pfn, unsigned long end_pfn); > > extern void initmem_init(void); > > +/* > + * Shadow stack pointer is moved by CALL, RET, and INCSSP(Q/D). INCSSPQ > + * moves shadow stack pointer up to 255 * 8 = ~2 KB (~1KB for INCSSPD) and > + * touches the first and the last element in the range, which triggers a > + * page fault if the range is not in a shadow stack. Because of this, > + * creating 4-KB guard pages around a shadow stack prevents these > + * instructions from going beyond. > + */ > +#define SHADOW_STACK_GUARD_GAP PAGE_SIZE The define is only used within arch/x86/mm/mmap.c. Maybe move it there? Otherwise: Reviewed-by: Kirill A. Shutemov -- Kirill A. Shutemov