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McKenney" , Boqun Feng , "H . Peter Anvin" , Paul Turner , linux-api@vger.kernel.org, Christian Brauner , Florian Weimer , David.Laight@ACULAB.COM, carlos@redhat.com, Peter Oskolkov , Alexander Mikhalitsyn , Chris Kennelly , Mathieu Desnoyers Subject: [PATCH 03/30] rseq: Introduce extensible rseq ABI Date: Tue, 22 Nov 2022 15:39:05 -0500 Message-Id: <20221122203932.231377-4-mathieu.desnoyers@efficios.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20221122203932.231377-1-mathieu.desnoyers@efficios.com> References: <20221122203932.231377-1-mathieu.desnoyers@efficios.com> MIME-Version: 1.0 X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RDNS_NONE,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1750230287789118096?= X-GMAIL-MSGID: =?utf-8?q?1750230287789118096?= Introduce the extensible rseq ABI, where the feature size supported by the kernel and the required alignment are communicated to user-space through ELF auxiliary vectors. This allows user-space to call rseq registration with a rseq_len of either 32 bytes for the original struct rseq size (which includes padding), or larger. If rseq_len is larger than 32 bytes, then it must be large enough to contain the feature size communicated to user-space through ELF auxiliary vectors. Signed-off-by: Mathieu Desnoyers --- Changes since v4: - Accept original rseq alignment for original rseq size. --- include/linux/sched.h | 4 ++++ kernel/ptrace.c | 2 +- kernel/rseq.c | 37 ++++++++++++++++++++++++++++++------- 3 files changed, 35 insertions(+), 8 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 23de7fe86cc4..2a9e14e3e668 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1305,6 +1305,7 @@ struct task_struct { #ifdef CONFIG_RSEQ struct rseq __user *rseq; + u32 rseq_len; u32 rseq_sig; /* * RmW on rseq_event_mask must be performed atomically @@ -2355,10 +2356,12 @@ static inline void rseq_fork(struct task_struct *t, unsigned long clone_flags) { if (clone_flags & CLONE_VM) { t->rseq = NULL; + t->rseq_len = 0; t->rseq_sig = 0; t->rseq_event_mask = 0; } else { t->rseq = current->rseq; + t->rseq_len = current->rseq_len; t->rseq_sig = current->rseq_sig; t->rseq_event_mask = current->rseq_event_mask; } @@ -2367,6 +2370,7 @@ static inline void rseq_fork(struct task_struct *t, unsigned long clone_flags) static inline void rseq_execve(struct task_struct *t) { t->rseq = NULL; + t->rseq_len = 0; t->rseq_sig = 0; t->rseq_event_mask = 0; } diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 54482193e1ed..0786450074c1 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -813,7 +813,7 @@ static long ptrace_get_rseq_configuration(struct task_struct *task, { struct ptrace_rseq_configuration conf = { .rseq_abi_pointer = (u64)(uintptr_t)task->rseq, - .rseq_abi_size = sizeof(*task->rseq), + .rseq_abi_size = task->rseq_len, .signature = task->rseq_sig, .flags = 0, }; diff --git a/kernel/rseq.c b/kernel/rseq.c index bda8175f8f99..c1058b3f10ac 100644 --- a/kernel/rseq.c +++ b/kernel/rseq.c @@ -18,6 +18,9 @@ #define CREATE_TRACE_POINTS #include +/* The original rseq structure size (including padding) is 32 bytes. */ +#define ORIG_RSEQ_SIZE 32 + #define RSEQ_CS_NO_RESTART_FLAGS (RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT | \ RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL | \ RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE) @@ -87,10 +90,15 @@ static int rseq_update_cpu_id(struct task_struct *t) u32 cpu_id = raw_smp_processor_id(); struct rseq __user *rseq = t->rseq; - if (!user_write_access_begin(rseq, sizeof(*rseq))) + if (!user_write_access_begin(rseq, t->rseq_len)) goto efault; unsafe_put_user(cpu_id, &rseq->cpu_id_start, efault_end); unsafe_put_user(cpu_id, &rseq->cpu_id, efault_end); + /* + * Additional feature fields added after ORIG_RSEQ_SIZE + * need to be conditionally updated only if + * t->rseq_len != ORIG_RSEQ_SIZE. + */ user_write_access_end(); trace_rseq_update(t); return 0; @@ -117,6 +125,11 @@ static int rseq_reset_rseq_cpu_id(struct task_struct *t) */ if (put_user(cpu_id, &t->rseq->cpu_id)) return -EFAULT; + /* + * Additional feature fields added after ORIG_RSEQ_SIZE + * need to be conditionally reset only if + * t->rseq_len != ORIG_RSEQ_SIZE. + */ return 0; } @@ -329,7 +342,7 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, /* Unregister rseq for current thread. */ if (current->rseq != rseq || !current->rseq) return -EINVAL; - if (rseq_len != sizeof(*rseq)) + if (rseq_len != current->rseq_len) return -EINVAL; if (current->rseq_sig != sig) return -EPERM; @@ -338,6 +351,7 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, return ret; current->rseq = NULL; current->rseq_sig = 0; + current->rseq_len = 0; return 0; } @@ -350,7 +364,7 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, * the provided address differs from the prior * one. */ - if (current->rseq != rseq || rseq_len != sizeof(*rseq)) + if (current->rseq != rseq || rseq_len != current->rseq_len) return -EINVAL; if (current->rseq_sig != sig) return -EPERM; @@ -359,15 +373,24 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, } /* - * If there was no rseq previously registered, - * ensure the provided rseq is properly aligned and valid. + * If there was no rseq previously registered, ensure the provided rseq + * is properly aligned, as communcated to user-space through the ELF + * auxiliary vector AT_RSEQ_ALIGN. If rseq_len is the original rseq + * size, the required alignment is the original struct rseq alignment. + * + * In order to be valid, rseq_len is either the original rseq size, or + * large enough to contain all supported fields, as communicated to + * user-space through the ELF auxiliary vector AT_RSEQ_FEATURE_SIZE. */ - if (!IS_ALIGNED((unsigned long)rseq, __alignof__(*rseq)) || - rseq_len != sizeof(*rseq)) + if (rseq_len < ORIG_RSEQ_SIZE || + (rseq_len == ORIG_RSEQ_SIZE && !IS_ALIGNED((unsigned long)rseq, ORIG_RSEQ_SIZE)) || + (rseq_len != ORIG_RSEQ_SIZE && (!IS_ALIGNED((unsigned long)rseq, __alignof__(*rseq)) || + rseq_len < offsetof(struct rseq, end)))) return -EINVAL; if (!access_ok(rseq, rseq_len)) return -EFAULT; current->rseq = rseq; + current->rseq_len = rseq_len; current->rseq_sig = sig; /* * If rseq was previously inactive, and has just been