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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 , Weijiang Yang , "Kirill A . Shutemov" , John Allen , kcc@google.com, eranian@google.com, rppt@kernel.org, jamorris@linux.microsoft.com, dethoma@microsoft.com, akpm@linux-foundation.org, Andrew.Cooper3@citrix.com, christina.schimpe@intel.com Cc: rick.p.edgecombe@intel.com Subject: [PATCH v5 23/39] mm: Don't allow write GUPs to shadow stack memory Date: Thu, 19 Jan 2023 13:23:01 -0800 Message-Id: <20230119212317.8324-24-rick.p.edgecombe@intel.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20230119212317.8324-1-rick.p.edgecombe@intel.com> References: <20230119212317.8324-1-rick.p.edgecombe@intel.com> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 93B1440010 X-Stat-Signature: otti79b3o9hhegn8kexetbpi46zcgeeo X-Rspam-User: X-HE-Tag: 1674163442-694418 X-HE-Meta: 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 j7jJ1e6J HqTeBmS2DZX0xPlmBVNs/QtdkPJ+yNHfGsNKfUlFouAAN0rcZMbFf/xPSLlwJ3rwbp0G1FdkM/MenoTUINUP0S6W/RU6CPH6/SUNOJCRUBegvNfoa45Ic1tsw+p7sAjUpbB1v1xPt4hAOvoX/clvJ4otKXe5YQHt9Ay1BbVTGfh9vvWyR1rKka+cYLUp2C+6P18ia/po+4ffxE2Le7lrswl9gkxeNRwSqNEr27mXV/gM03gVTjnE51GyaeZnNpZb6SWLtPr7FOagmzdxnef7xtyN8LSEwseNgOcvj 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: The x86 Control-flow Enforcement Technology (CET) feature includes a new type of memory called shadow stack. This shadow stack memory has some unusual properties, which requires some core mm changes to function properly. Shadow stack memory is writable only in very specific, controlled ways. However, since it is writable, the kernel treats it as such. As a result there remain many ways for userspace to trigger the kernel to write to shadow stack's via get_user_pages(, FOLL_WRITE) operations. To make this a little less exposed, block writable GUPs for shadow stack VMAs. Still allow FOLL_FORCE to write through shadow stack protections, as it does for read-only protections. Reviewed-by: Kees Cook Tested-by: Pengfei Xu Tested-by: John Allen Signed-off-by: Rick Edgecombe --- v3: - Add comment in __pte_access_permitted() (Dave) - Remove unneeded shadow stack specific check in __pte_access_permitted() (Jann) arch/x86/include/asm/pgtable.h | 5 +++++ mm/gup.c | 2 +- 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h index 87d3068734ec..425ded5dd6ec 100644 --- a/arch/x86/include/asm/pgtable.h +++ b/arch/x86/include/asm/pgtable.h @@ -1671,6 +1671,11 @@ static inline bool __pte_access_permitted(unsigned long pteval, bool write) { unsigned long need_pte_bits = _PAGE_PRESENT|_PAGE_USER; + /* + * Write=0,Dirty=1 PTEs are shadow stack, which the kernel + * shouldn't generally allow access to, but since they + * are already Write=0, the below logic covers both cases. + */ if (write) need_pte_bits |= _PAGE_RW; diff --git a/mm/gup.c b/mm/gup.c index f45a3a5be53a..bfd33d9edb89 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -982,7 +982,7 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags) return -EFAULT; if (write) { - if (!(vm_flags & VM_WRITE)) { + if (!(vm_flags & VM_WRITE) || (vm_flags & VM_SHADOW_STACK)) { if (!(gup_flags & FOLL_FORCE)) return -EFAULT; /* hugetlb does not support FOLL_FORCE|FOLL_WRITE. */ -- 2.17.1