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bpf: add crosstask check to __bpf_get_stack #644

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bpf: add crosstask check to __bpf_get_stack #644

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3 changes: 3 additions & 0 deletions include/uapi/linux/bpf.h
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Original file line number Diff line number Diff line change
Expand Up @@ -4517,6 +4517,8 @@ 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*.
Expand All @@ -4528,6 +4530,7 @@ 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.
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11 changes: 10 additions & 1 deletion kernel/bpf/stackmap.c
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Original file line number Diff line number Diff line change
Expand Up @@ -388,6 +388,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
{
u32 trace_nr, copy_len, elem_size, num_elem, max_depth;
bool user_build_id = flags & BPF_F_USER_BUILD_ID;
bool crosstask = task && task != current;
u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
bool user = flags & BPF_F_USER_STACK;
struct perf_callchain_entry *trace;
Expand All @@ -410,6 +411,14 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
if (task && user && !user_mode(regs))
goto err_fault;

/* get_perf_callchain does not support crosstask user stack walking
* but returns an empty stack instead of NULL.
*/
if (crosstask && user) {
err = -EOPNOTSUPP;
goto clear;
}

num_elem = size / elem_size;
max_depth = num_elem + skip;
if (sysctl_perf_event_max_stack < max_depth)
Expand All @@ -421,7 +430,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
trace = get_callchain_entry_for_task(task, max_depth);
else
trace = get_perf_callchain(regs, 0, kernel, user, max_depth,
false, false);
crosstask, false);
if (unlikely(!trace))
goto err_fault;

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3 changes: 3 additions & 0 deletions tools/include/uapi/linux/bpf.h
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Original file line number Diff line number Diff line change
Expand Up @@ -4517,6 +4517,8 @@ 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*.
Expand All @@ -4528,6 +4530,7 @@ 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.
Expand Down