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bpf: Ensure RCU lock is held around bpf_prog_ksym_find

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Add a warning to ensure RCU lock is held around tree lookup, and then
fix one of the invocations in bpf_stack_walker. The program has an
active stack frame and won't disappear. Use the opportunity to remove
unneeded invocation of is_bpf_text_address.

Fixes: f18b03faba ("bpf: Implement BPF exceptions")
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20250703204818.925464-5-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Kumar Kartikeya Dwivedi 2025-07-03 13:48:10 -07:00 committed by Alexei Starovoitov
parent 0e521efaf3
commit d090326860
2 changed files with 13 additions and 3 deletions
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5
kernel/bpf/core.c
View File

@ -782,7 +782,10 @@ bool is_bpf_text_address(unsigned long addr)
struct bpf_prog *bpf_prog_ksym_find(unsigned long addr)
{
struct bpf_ksym *ksym = bpf_ksym_find(addr);
struct bpf_ksym *ksym;
WARN_ON_ONCE(!rcu_read_lock_held());
ksym = bpf_ksym_find(addr);
return ksym && ksym->prog ?
container_of(ksym, struct bpf_prog_aux, ksym)->prog :

11
kernel/bpf/helpers.c
View File

@ -2981,9 +2981,16 @@ static bool bpf_stack_walker(void *cookie, u64 ip, u64 sp, u64 bp)
struct bpf_throw_ctx *ctx = cookie;
struct bpf_prog *prog;
if (!is_bpf_text_address(ip))
return !ctx->cnt;
/*
* The RCU read lock is held to safely traverse the latch tree, but we
* don't need its protection when accessing the prog, since it has an
* active stack frame on the current stack trace, and won't disappear.
*/
rcu_read_lock();
prog = bpf_prog_ksym_find(ip);
rcu_read_unlock();
if (!prog)
return !ctx->cnt;
ctx->cnt++;
if (bpf_is_subprog(prog))
return true;