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Wed, 03 Apr 2024 16:42:04 -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, conor@kernel.org Cc: 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, corbet@lwn.net, 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 v3 13/29] riscv mmu: write protect and shadow stack Date: Wed, 3 Apr 2024 16:35:01 -0700 Message-ID: <20240403234054.2020347-14-debug@rivosinc.com> X-Mailer: git-send-email 2.43.2 In-Reply-To: <20240403234054.2020347-1-debug@rivosinc.com> References: <20240403234054.2020347-1-debug@rivosinc.com> MIME-Version: 1.0 X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 9A54514000A X-Stat-Signature: fkgufoe76d637aqf5x1zd1dar47o9ngo X-Rspam-User: X-HE-Tag: 1712187725-660321 X-HE-Meta: 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 VoqPwymh 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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 Reviewed-by: 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 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