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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , linux-riscv@lists.infradead.org Subject: [PATCH RFC v3 2/6] riscv/mm: add untagged_addr_remote_unlocked() Date: Fri, 17 Jul 2026 13:00:32 -0400 Message-ID: <20260717170036.743149-3-riel@surriel.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260717170036.743149-1-riel@surriel.com> References: <20260717170036.743149-1-riel@surriel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: A46942000A X-Rspam-User: X-Stat-Signature: wiuw9qdboisf118prrxeca7cznidk6go X-Rspamd-Server: rspam03 X-HE-Tag: 1784307666-8535 X-HE-Meta: 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 UG5YWN38 omUiqoMeTbax8PqWTdzIEntLlhKdnDxW8Th+JCDucd3qb8FnOGTOm9uCZmGjpdINd9x3TbaQvZkjIu8IDS+0AehoXYQ528I7rXgllBcFtXPN6BGjzZvs4ZjwSe7oTE1cFF8bDnRqpgJtvE1XaOEIMSR2BYspFElOwA+7ZTyUvLsy4v3eOHbvnpp0a2C8AACIPf9iNkYhOrTcY5OVHb8eTsVd1l4jgXpSkEUSGDelJF7eRVPwpp5d4f7u1G4nOTNp/3HswxD4j3H+Q/sNx7BybuaVOlestfN6QWbfJ+i8wD233PoW8Q5nJKoHiEDUj/LkQwrpH Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: __access_remote_vm() untags the remote address before looking up the VMA, now without holding the mmap lock. riscv defines untagged_addr_remote() but not untagged_addr_remote_unlocked(), so it falls back to the generic version, which untags with untagged_addr(). That reads current->mm, not the target mm, so a remote access to a process using pointer masking would untag with the wrong mask. mm->context.pmlen is set only through PR_SET_TAGGED_ADDR_CTRL and is stable afterwards, so it can be read without the mmap lock, as it already is from untagged_addr() and mm_untag_mask(). Add untagged_addr_remote_unlocked(), which untags against the target mm, and annotate context.pmlen accesses with READ_ONCE() and WRITE_ONCE() so the lockless reads are explicit and KCSAN-clean. untagged_addr_remote() keeps its mmap_assert_locked() and shares the code. Assisted-by: Claude:claude-opus-4.8 Signed-off-by: Rik van Riel --- arch/riscv/include/asm/mmu_context.h | 4 ++-- arch/riscv/include/asm/uaccess.h | 10 +++++++--- arch/riscv/kernel/process.c | 12 +++++++----- 3 files changed, 16 insertions(+), 10 deletions(-) diff --git a/arch/riscv/include/asm/mmu_context.h b/arch/riscv/include/asm/mmu_context.h index dbf27a78df6c..3ce16796e5a2 100644 --- a/arch/riscv/include/asm/mmu_context.h +++ b/arch/riscv/include/asm/mmu_context.h @@ -21,7 +21,7 @@ static inline void activate_mm(struct mm_struct *prev, struct mm_struct *next) { #ifdef CONFIG_RISCV_ISA_SUPM - next->context.pmlen = 0; + WRITE_ONCE(next->context.pmlen, 0); #endif switch_mm(prev, next, NULL); } @@ -44,7 +44,7 @@ DECLARE_STATIC_KEY_FALSE(use_asid_allocator); #define mm_untag_mask mm_untag_mask static inline unsigned long mm_untag_mask(struct mm_struct *mm) { - return -1UL >> mm->context.pmlen; + return -1UL >> READ_ONCE(mm->context.pmlen); } #endif diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h index 5d4ec15584cf..53806e0f7dcf 100644 --- a/arch/riscv/include/asm/uaccess.h +++ b/arch/riscv/include/asm/uaccess.h @@ -16,7 +16,7 @@ static inline unsigned long __untagged_addr_remote(struct mm_struct *mm, unsigned long addr) { if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM)) { - u8 pmlen = mm->context.pmlen; + u8 pmlen = READ_ONCE(mm->context.pmlen); /* Virtual addresses are sign-extended; physical addresses are zero-extended. */ if (IS_ENABLED(CONFIG_MMU)) @@ -33,12 +33,16 @@ static inline unsigned long __untagged_addr_remote(struct mm_struct *mm, unsigne (__force __typeof__(addr))__untagged_addr_remote(current->mm, __addr); \ }) -#define untagged_addr_remote(mm, addr) ({ \ +#define untagged_addr_remote_unlocked(mm, addr) ({ \ unsigned long __addr = (__force unsigned long)(addr); \ - mmap_assert_locked(mm); \ (__force __typeof__(addr))__untagged_addr_remote(mm, __addr); \ }) +#define untagged_addr_remote(mm, addr) ({ \ + mmap_assert_locked(mm); \ + untagged_addr_remote_unlocked(mm, addr); \ +}) + #define access_ok(addr, size) likely(__access_ok(untagged_addr(addr), size)) #else #define untagged_addr(addr) (addr) diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c index b2df7f72241a..6ae7552fed09 100644 --- a/arch/riscv/kernel/process.c +++ b/arch/riscv/kernel/process.c @@ -357,13 +357,15 @@ long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg) if (mmap_write_lock_killable(mm)) return -EINTR; - if (test_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags) && mm->context.pmlen != pmlen) { - mmap_write_unlock(mm); - return -EBUSY; + if (test_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags)) { + if (READ_ONCE(mm->context.pmlen) != pmlen) { + mmap_write_unlock(mm); + return -EBUSY; + } } envcfg_update_bits(task, ENVCFG_PMM, pmm); - mm->context.pmlen = pmlen; + WRITE_ONCE(mm->context.pmlen, pmlen); mmap_write_unlock(mm); @@ -394,7 +396,7 @@ long get_tagged_addr_ctrl(struct task_struct *task) break; } - if (task->mm->context.pmlen) + if (READ_ONCE(task->mm->context.pmlen)) ret |= PR_TAGGED_ADDR_ENABLE; return ret; -- 2.53.0-Meta