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Peter Anvin" , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Lorenzo Stoakes , Paul Walmsley , Palmer Dabbelt , Albert Ou , Conor Dooley , Rob Herring , Krzysztof Kozlowski , Arnd Bergmann , Christian Brauner , Peter Zijlstra , Oleg Nesterov , Eric Biederman , Kees Cook , Jonathan Corbet , Shuah Khan Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, devicetree@vger.kernel.org, linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, alistair.francis@wdc.com, richard.henderson@linaro.org, jim.shu@sifive.com, andybnac@gmail.com, kito.cheng@sifive.com, charlie@rivosinc.com, atishp@rivosinc.com, evan@rivosinc.com, cleger@rivosinc.com, alexghiti@rivosinc.com, samitolvanen@google.com, broonie@kernel.org, rick.p.edgecombe@intel.com, Deepak Gupta X-Mailer: b4 0.14.0 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 36BED18000F X-Stat-Signature: ozkx8pq18bpwan3ejoyr7ozeda1544p7 X-Rspam-User: X-HE-Tag: 1727798859-474189 X-HE-Meta: U2FsdGVkX1/fAg7aOcuWIuGGovRYsagfMSq9JPISu/FFBMz2otdckWGXJYGuHh0ufS2n09jDfyGfHdq1DSr/Cv7rYFknZBjP2sH/0If4nd9+EZ/qcn/jhbQXfSed3ZifG4d15kiqGUsr7Zu0ES/oZZblll4wESKCqpsa7d4qNlNVfDsXdvFW2Z4Tms3V5FJvWbTUkmeMZrnjy8zL/GRGO+3Mu9JV5nFJuumXsxNfNVlWMOXAEouh9Vr6ryNbSv6vVP+qRdZV39w9JT4N78PGHxvcdo8oHEITXzy9Bme7whT11N0BlX3R537l0RYaBfGbYR3AHwfEvkO3XhYoamzIIFT4q2w/Tepw5OALFKr6ehxImXVavcYTea1i3Ah3yi+ryoLJtD0Z0Kz+kstVuMz300Scm1A5AadQtIs81eTaCYmstOmE0Kra6/ByePthxBF7fCHR6zUbYEIT2i9ESXFP4uKsIqbATAlptajY+jPE3xHh5p39dHZmtRUaW6rw7gTwrH7nehpIL6nIOtBJPgajxe51o+IE7n9JRxED8Yc8nHBo9UrX3gcFBl4rxefPgITx+Fif4xLx2Nq/lqvpsbG+vI4tVCEilcZiyqS49/0ImE/Y1hrfCix1t4/gayHhdSQIf+5r/ybUZsXUEHazHXwPpGNealslapycxa5UJLlp64oErhQG4DUFMzJ1b7uHIuN066tLRuME4WhlzVWZsIobJrF4A8jktZ7w4vQ4sRkrnVC6DUaJDWGsMocNUn185p2krMjPikK3VmdNvGOlkr5gMo6lmc/k6EE9D2IaE4QQQHx3qC3oqyTUmrwUmjWCqZ6PtXBpxYC6H8PSrL542fIgrQYvYEstH2HXRJK4y9cu1oPmElbK+ZjAUnwFRbnidGLjcgR8K4ydZYayfaNfu4U8kmUtwrQFiOBNM1bxB7bLToFWBTyB1TT0a07J0p+/meyU0pqXZsnGTqZmYud2hs2 cQq72P4I p5+5mLvaUFFPVBs8Y8sK7tRciygBKEOALNMwdqaFqn5ZJV9sWqSLf4rsooAeC9FicXiD4WqTwy/SR3HfJj4V9KQ/BnHw1ELfdOD6I5dw3cYmdOuTBscxrLnTZ7fHMxfBVR5RFSZ0534WH1kQZ2052jiYc7ahvHUuapETVy4kLJCZpIepmYf/cEy9mTg9CcUgfA97gKMDq+e0wXVMtTWsBsH0w+f8EevlRN2c+qpxPohHNWYILE6LfTIJLZQotv3Z7B6i/khkFDyo1fq1/qRtHTe8sUSydGggl8XollHPAW2ZI9nhzs4jC8LTGsgvM4QuLXoOea7apqet+ddrLQ6AqxXhG9F47FEXjMrhviCg0EurubhSv1CcvjHg7ryiaSHD0pQZVt5h4xhpZa5QE3er5vcKnww/ycup3IKfNXDhXRc+3UQt6PR1nAjajwlK06uKvzCUuJxTor53/u1aVMrUKR+uPD7jk73kamEi4c30Za8laOY7873kcc7rDWzZFIlXvqGGWuDopyTqPwmuo8NRfiV9wXwA/R2hIENd0ruCH5BFSYMvRiHsn8qtwoDf+C9nJxVEeABgyuCU2vvU= 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 shadow stack 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 Alexandre Ghiti --- 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 7963ab11d924..fdab7d74437d 100644 --- a/arch/riscv/include/asm/pgtable.h +++ b/arch/riscv/include/asm/pgtable.h @@ -411,7 +411,7 @@ static inline int pte_devmap(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) */ @@ -612,7 +612,15 @@ 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); + pte_t read_pte = READ_ONCE(*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