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authorMathieu Desnoyers <mathieu.desnoyers@efficios.com>2022-11-22 15:39:05 -0500
committerPeter Zijlstra <peterz@infradead.org>2022-12-27 12:52:10 +0100
commitee3e3ac05c2631ce1f12d88c9cc9a092f8fe947a (patch)
treee0c6d2672012d5e85edf1b6d633c27d34aec3382 /kernel/rseq.c
parent317c8194e6aeb8b3b573ad139fc2a0635856498e (diff)
rseq: Introduce extensible rseq ABI
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 <mathieu.desnoyers@efficios.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20221122203932.231377-4-mathieu.desnoyers@efficios.com
Diffstat (limited to 'kernel/rseq.c')
-rw-r--r--kernel/rseq.c37
1 files changed, 30 insertions, 7 deletions
diff --git a/kernel/rseq.c b/kernel/rseq.c
index d38ab944105d..7962738455c9 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -18,6 +18,9 @@
#define CREATE_TRACE_POINTS
#include <trace/events/rseq.h>
+/* 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;
}
@@ -344,7 +357,7 @@ 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;
@@ -353,6 +366,7 @@ 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;
}
@@ -365,7 +379,7 @@ 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;
@@ -374,15 +388,24 @@ 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