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Thu, 28 Mar 2024 21:46:24 -0700 (PDT) From: Deepak Gupta To: paul.walmsley@sifive.com, rick.p.edgecombe@intel.com, broonie@kernel.org, Szabolcs.Nagy@arm.com, kito.cheng@sifive.com, keescook@chromium.org, ajones@ventanamicro.com, conor.dooley@microchip.com, cleger@rivosinc.com, atishp@atishpatra.org, alex@ghiti.fr, bjorn@rivosinc.com, alexghiti@rivosinc.com, samuel.holland@sifive.com, palmer@sifive.com, conor@kernel.org, linux-doc@vger.kernel.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-kselftest@vger.kernel.org Cc: corbet@lwn.net, tech-j-ext@lists.risc-v.org, palmer@dabbelt.com, aou@eecs.berkeley.edu, robh+dt@kernel.org, krzysztof.kozlowski+dt@linaro.org, oleg@redhat.com, akpm@linux-foundation.org, arnd@arndb.de, ebiederm@xmission.com, Liam.Howlett@oracle.com, vbabka@suse.cz, lstoakes@gmail.com, shuah@kernel.org, brauner@kernel.org, debug@rivosinc.com, andy.chiu@sifive.com, jerry.shih@sifive.com, hankuan.chen@sifive.com, greentime.hu@sifive.com, evan@rivosinc.com, xiao.w.wang@intel.com, charlie@rivosinc.com, apatel@ventanamicro.com, mchitale@ventanamicro.com, dbarboza@ventanamicro.com, sameo@rivosinc.com, shikemeng@huaweicloud.com, willy@infradead.org, vincent.chen@sifive.com, guoren@kernel.org, samitolvanen@google.com, songshuaishuai@tinylab.org, gerg@kernel.org, heiko@sntech.de, bhe@redhat.com, jeeheng.sia@starfivetech.com, cyy@cyyself.name, maskray@google.com, ancientmodern4@gmail.com, mathis.salmen@matsal.de, cuiyunhui@bytedance.com, bgray@linux.ibm.com, mpe@ellerman.id.au, baruch@tkos.co.il, alx@kernel.org, david@redhat.com, catalin.marinas@arm.com, revest@chromium.org, josh@joshtriplett.org, shr@devkernel.io, deller@gmx.de, omosnace@redhat.com, ojeda@kernel.org, jhubbard@nvidia.com Subject: [PATCH v2 12/27] riscv mmu: write protect and shadow stack Date: Thu, 28 Mar 2024 21:44:44 -0700 Message-Id: <20240329044459.3990638-13-debug@rivosinc.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240329044459.3990638-1-debug@rivosinc.com> References: <20240329044459.3990638-1-debug@rivosinc.com> MIME-Version: 1.0 X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 5CF19100002 X-Stat-Signature: syi5fqzh5nbgsxmejzmy8wobfa9oydrd X-Rspam-User: X-HE-Tag: 1711687586-232416 X-HE-Meta: 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 Usp69NxH 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 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: List-Subscribe: List-Unsubscribe: `fork` implements copy on write (COW) by making pages readonly in child and parent both. ptep_set_wrprotect and pte_wrprotect clears _PAGE_WRITE in PTE. Assumption is that page is readable and on fault copy on write happens. To implement COW on such pages, clearing up W bit makes them XWR = 000. This will result in wrong PTE setting which says no perms but V=1 and PFN field pointing to final page. Instead desired behavior is to turn it into a readable page, take an access (load/store) fault on sspush/sspop (shadow stack) and then perform COW on such pages. This way regular reads would still be allowed and not lead to COW maintaining current behavior of COW on non-shadow stack but writeable memory. On the other hand it doesn't interfere with existing COW for read-write memory. Assumption is always that _PAGE_READ must have been set and thus setting _PAGE_READ is harmless. Signed-off-by: Deepak Gupta --- arch/riscv/include/asm/pgtable.h | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h index 9b837239d3e8..7a1c2a98d272 100644 --- a/arch/riscv/include/asm/pgtable.h +++ b/arch/riscv/include/asm/pgtable.h @@ -398,7 +398,7 @@ static inline int pte_special(pte_t pte) static inline pte_t pte_wrprotect(pte_t pte) { - return __pte(pte_val(pte) & ~(_PAGE_WRITE)); + return __pte((pte_val(pte) & ~(_PAGE_WRITE)) | (_PAGE_READ)); } /* static inline pte_t pte_mkread(pte_t pte) */ @@ -581,7 +581,15 @@ static inline pte_t ptep_get_and_clear(struct mm_struct *mm, static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long address, pte_t *ptep) { - atomic_long_and(~(unsigned long)_PAGE_WRITE, (atomic_long_t *)ptep); + volatile pte_t read_pte = *ptep; + /* + * ptep_set_wrprotect can be called for shadow stack ranges too. + * shadow stack memory is XWR = 010 and thus clearing _PAGE_WRITE will lead to + * encoding 000b which is wrong encoding with V = 1. This should lead to page fault + * but we dont want this wrong configuration to be set in page tables. + */ + atomic_long_set((atomic_long_t *)ptep, + ((pte_val(read_pte) & ~(unsigned long)_PAGE_WRITE) | _PAGE_READ)); } #define __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH