diff options
| author | Oleg Nesterov <oleg@redhat.com> | 2024-08-01 15:27:09 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2024-08-02 11:30:30 +0200 |
| commit | 84455e6923c79a37812930787aaa141e82afe315 (patch) | |
| tree | b7096be1b261a75c1e08f64e6801d66b016086c4 /kernel/events | |
| parent | perf,x86: avoid missing caller address in stack traces captured in uprobe (diff) | |
| download | linux-84455e6923c79a37812930787aaa141e82afe315.tar.xz linux-84455e6923c79a37812930787aaa141e82afe315.zip | |
uprobes: document the usage of mm->mmap_lock
The comment above uprobe_write_opcode() is wrong, unapply_uprobe() calls
it under mmap_read_lock() and this is correct.
And it is completely unclear why register_for_each_vma() takes mmap_lock
for writing, add a comment to explain that mmap_write_lock() is needed to
avoid the following race:
- A task T hits the bp installed by uprobe and calls
find_active_uprobe()
- uprobe_unregister() removes this uprobe/bp
- T calls find_uprobe() which returns NULL
- another uprobe_register() installs the bp at the same address
- T calls is_trap_at_addr() which returns true
- T returns to handle_swbp() and gets SIGTRAP.
Reported-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Link: https://lore.kernel.org/r/20240801132709.GA8780@redhat.com
Diffstat (limited to 'kernel/events')
| -rw-r--r-- | kernel/events/uprobes.c | 10 |
1 files changed, 8 insertions, 2 deletions
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index f69ecd39b1a8..2d1457eee965 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -453,7 +453,7 @@ static int update_ref_ctr(struct uprobe *uprobe, struct mm_struct *mm, * @vaddr: the virtual address to store the opcode. * @opcode: opcode to be written at @vaddr. * - * Called with mm->mmap_lock held for write. + * Called with mm->mmap_lock held for read or write. * Return 0 (success) or a negative errno. */ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm, @@ -1046,7 +1046,13 @@ register_for_each_vma(struct uprobe *uprobe, struct uprobe_consumer *new) if (err && is_register) goto free; - + /* + * We take mmap_lock for writing to avoid the race with + * find_active_uprobe() which takes mmap_lock for reading. + * Thus this install_breakpoint() can not make + * is_trap_at_addr() true right after find_uprobe() + * returns NULL in find_active_uprobe(). + */ mmap_write_lock(mm); vma = find_vma(mm, info->vaddr); if (!vma || !valid_vma(vma, is_register) || |