From: Peter Zijlstra Date: Tue, 28 Feb 2017 17:18:01 +0000 (-0800) Subject: perf/core: Fix concurrent sys_perf_event_open() vs. 'move_group' race X-Git-Tag: v4.1.12-98.0.20170517_2143~44^2 X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=7a2038b000f6dd85f8e985c746ea4fa9c0728677;p=users%2Fjedix%2Flinux-maple.git perf/core: Fix concurrent sys_perf_event_open() vs. 'move_group' race Di Shen reported a race between two concurrent sys_perf_event_open() calls where both try and move the same pre-existing software group into a hardware context. The problem is exactly that described in commit: f63a8daa5812 ("perf: Fix event->ctx locking") ... where, while we wait for a ctx->mutex acquisition, the event->ctx relation can have changed under us. That very same commit failed to recognise sys_perf_event_context() as an external access vector to the events and thereby didn't apply the established locking rules correctly. So while one sys_perf_event_open() call is stuck waiting on mutex_lock_double(), the other (which owns said locks) moves the group about. So by the time the former sys_perf_event_open() acquires the locks, the context we've acquired is stale (and possibly dead). Apply the established locking rules as per perf_event_ctx_lock_nested() to the mutex_lock_double() for the 'move_group' case. This obviously means we need to validate state after we acquire the locks. Reported-by: Di Shen (Keen Lab) Tested-by: John Dias Signed-off-by: Peter Zijlstra (Intel) Cc: Alexander Shishkin Cc: Arnaldo Carvalho de Melo Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Kees Cook Cc: Linus Torvalds Cc: Min Chong Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Fixes: f63a8daa5812 ("perf: Fix event->ctx locking") Link: http://lkml.kernel.org/r/20170106131444.GZ3174@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar (cherry picked from commit 321027c1fe77f892f4ea07846aeae08cefbbb290) Duplicate perf events are handled by setting appropriate return value and redirecting the flow to 'err_locked' goto label followed by 'err_context' label. In UEK4, 'err_locked' goto label is not available. Hence, the operations under this label are performed before redirecting the flow to 'err_context' label. Orabug : 25564210 CVE-2017-6001 Signed-off-by: Ashok Vairavan Reviewed-by: Ethan Zhao Signed-off-by: Dhaval Giani --- diff --git a/kernel/events/core.c b/kernel/events/core.c index eddf1ed4155ea..2f64ec92f4324 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -7862,6 +7862,38 @@ static int perf_event_set_clock(struct perf_event *event, clockid_t clk_id) return 0; } +/* + * Variation on perf_event_ctx_lock_nested(), except we take two context + * mutexes. + */ +static struct perf_event_context * +__perf_event_ctx_lock_double(struct perf_event *group_leader, + struct perf_event_context *ctx) +{ + struct perf_event_context *gctx; + +again: + rcu_read_lock(); + gctx = READ_ONCE(group_leader->ctx); + if (!atomic_inc_not_zero(&gctx->refcount)) { + rcu_read_unlock(); + goto again; + } + rcu_read_unlock(); + + mutex_lock_double(&gctx->mutex, &ctx->mutex); + + if (group_leader->ctx != gctx) { + mutex_unlock(&ctx->mutex); + mutex_unlock(&gctx->mutex); + put_ctx(gctx); + goto again; + } + + return gctx; +} + + /** * sys_perf_event_open - open a performance event, associate it to a task/cpu * @@ -8087,13 +8119,7 @@ SYSCALL_DEFINE5(perf_event_open, } if (move_group) { - gctx = group_leader->ctx; - - /* - * See perf_event_ctx_lock() for comments on the details - * of swizzling perf_event::ctx. - */ - mutex_lock_double(&gctx->mutex, &ctx->mutex); + gctx = __perf_event_ctx_lock_double(group_leader, ctx); perf_remove_from_context(group_leader, false); @@ -8152,10 +8178,8 @@ SYSCALL_DEFINE5(perf_event_open, perf_install_in_context(ctx, event, event->cpu); perf_unpin_context(ctx); - if (move_group) { - mutex_unlock(&gctx->mutex); - put_ctx(gctx); - } + if (move_group) + perf_event_ctx_unlock(group_leader, gctx); mutex_unlock(&ctx->mutex); put_online_cpus();