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* [PATCH bpf-next v5 1/9] bpf: Fix bpf_strtol and bpf_strtoul helpers for 32bit
@ 2024-09-13 19:17 Daniel Borkmann
  2024-09-13 19:17 ` [PATCH bpf-next v5 2/9] bpf: Remove truncation test in bpf_strtol and bpf_strtoul helpers Daniel Borkmann
                   ` (8 more replies)
  0 siblings, 9 replies; 10+ messages in thread
From: Daniel Borkmann @ 2024-09-13 19:17 UTC (permalink / raw)
  To: bpf; +Cc: shung-hsi.yu, andrii, ast, kongln9170, Daniel Borkmann

The bpf_strtol() and bpf_strtoul() helpers are currently broken on 32bit:

The argument type ARG_PTR_TO_LONG is BPF-side "long", not kernel-side "long"
and therefore always considered fixed 64bit no matter if 64 or 32bit underlying
architecture.

This contract breaks in case of the two mentioned helpers since their BPF_CALL
definition for the helpers was added with {unsigned,}long *res. Meaning, the
transition from BPF-side "long" (BPF program) to kernel-side "long" (BPF helper)
breaks here.

Both helpers call __bpf_strtoll() with "long long" correctly, but later assigning
the result into 32-bit "*(long *)" on 32bit architectures. From a BPF program
point of view, this means upper bits will be seen as uninitialised.

Therefore, fix both BPF_CALL signatures to {s,u}64 types to fix this situation.

Now, changing also uapi/bpf.h helper documentation which generates bpf_helper_defs.h
for BPF programs is tricky: Changing signatures there to __{s,u}64 would trigger
compiler warnings (incompatible pointer types passing 'long *' to parameter of type
'__s64 *' (aka 'long long *')) for existing BPF programs.

Leaving the signatures as-is would be fine as from BPF program point of view it is
still BPF-side "long" and thus equivalent to __{s,u}64 on 64 or 32bit underlying
architectures.

Note that bpf_strtol() and bpf_strtoul() are the only helpers with this issue.

Fixes: d7a4cb9b6705 ("bpf: Introduce bpf_strtol and bpf_strtoul helpers")
Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/481fcec8-c12c-9abb-8ecb-76c71c009959@iogearbox.net
---
 v3 -> v4:
 - added patch

 kernel/bpf/helpers.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 3956be5d6440..0cf42be52890 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -518,7 +518,7 @@ static int __bpf_strtoll(const char *buf, size_t buf_len, u64 flags,
 }
 
 BPF_CALL_4(bpf_strtol, const char *, buf, size_t, buf_len, u64, flags,
-	   long *, res)
+	   s64 *, res)
 {
 	long long _res;
 	int err;
@@ -543,7 +543,7 @@ const struct bpf_func_proto bpf_strtol_proto = {
 };
 
 BPF_CALL_4(bpf_strtoul, const char *, buf, size_t, buf_len, u64, flags,
-	   unsigned long *, res)
+	   u64 *, res)
 {
 	unsigned long long _res;
 	bool is_negative;
-- 
2.43.0


^ permalink raw reply related	[flat|nested] 10+ messages in thread
end of thread, other threads:[~2024-09-13 20:31 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2024-09-13 19:17 [PATCH bpf-next v5 1/9] bpf: Fix bpf_strtol and bpf_strtoul helpers for 32bit Daniel Borkmann
2024-09-13 19:17 ` [PATCH bpf-next v5 2/9] bpf: Remove truncation test in bpf_strtol and bpf_strtoul helpers Daniel Borkmann
2024-09-13 19:17 ` [PATCH bpf-next v5 3/9] bpf: Fix helper writes to read-only maps Daniel Borkmann
2024-09-13 19:17 ` [PATCH bpf-next v5 4/9] bpf: Improve check_raw_mode_ok test for MEM_UNINIT-tagged types Daniel Borkmann
2024-09-13 19:17 ` [PATCH bpf-next v5 5/9] bpf: Zero former ARG_PTR_TO_{LONG,INT} args in case of error Daniel Borkmann
2024-09-13 19:17 ` [PATCH bpf-next v5 6/9] selftests/bpf: Fix ARG_PTR_TO_LONG {half-,}uninitialized test Daniel Borkmann
2024-09-13 19:17 ` [PATCH bpf-next v5 7/9] selftests/bpf: Rename ARG_PTR_TO_LONG test description Daniel Borkmann
2024-09-13 19:17 ` [PATCH bpf-next v5 8/9] selftests/bpf: Add a test case to write strtol result into .rodata Daniel Borkmann
2024-09-13 19:17 ` [PATCH bpf-next v5 9/9] selftests/bpf: Add a test case to write mtu " Daniel Borkmann
2024-09-13 20:31 ` [PATCH bpf-next v5 1/9] bpf: Fix bpf_strtol and bpf_strtoul helpers for 32bit patchwork-bot+netdevbpf

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