From a341738951bf71c19df7fb620c2f58c2ea869502 Mon Sep 17 00:00:00 2001 From: Jordan Rome Date: Wed, 8 Nov 2023 03:23:34 -0800 Subject: bpf: Add crosstask check to __bpf_get_stack [ Upstream commit b8e3a87a627b575896e448021e5c2f8a3bc19931 ] Currently get_perf_callchain only supports user stack walking for the current task. Passing the correct *crosstask* param will return 0 frames if the task passed to __bpf_get_stack isn't the current one instead of a single incorrect frame/address. This change passes the correct *crosstask* param but also does a preemptive check in __bpf_get_stack if the task is current and returns -EOPNOTSUPP if it is not. This issue was found using bpf_get_task_stack inside a BPF iterator ("iter/task"), which iterates over all tasks. bpf_get_task_stack works fine for fetching kernel stacks but because get_perf_callchain relies on the caller to know if the requested *task* is the current one (via *crosstask*) it was failing in a confusing way. It might be possible to get user stacks for all tasks utilizing something like access_process_vm but that requires the bpf program calling bpf_get_task_stack to be sleepable and would therefore be a breaking change. Fixes: fa28dcb82a38 ("bpf: Introduce helper bpf_get_task_stack()") Signed-off-by: Jordan Rome Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20231108112334.3433136-1-jordalgo@meta.com Signed-off-by: Sasha Levin --- include/uapi/linux/bpf.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'include/uapi/linux') diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 0448700890f7..ada7acb91a1b 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -4490,6 +4490,8 @@ union bpf_attr { * long bpf_get_task_stack(struct task_struct *task, void *buf, u32 size, u64 flags) * Description * Return a user or a kernel stack in bpf program provided buffer. + * Note: the user stack will only be populated if the *task* is + * the current task; all other tasks will return -EOPNOTSUPP. * To achieve this, the helper needs *task*, which is a valid * pointer to **struct task_struct**. To store the stacktrace, the * bpf program provides *buf* with a nonnegative *size*. @@ -4501,6 +4503,7 @@ union bpf_attr { * * **BPF_F_USER_STACK** * Collect a user space stack instead of a kernel stack. + * The *task* must be the current task. * **BPF_F_USER_BUILD_ID** * Collect buildid+offset instead of ips for user stack, * only valid if **BPF_F_USER_STACK** is also specified. -- cgit v1.2.3