On 6/2/23 3:50 PM, Arnd Bergmann wrote:

From: Arnd Bergmann arnd@arndb.de

bpf_probe_read_kernel() has a __weak definition in core.c and another definition with an incompatible prototype in kernel/trace/bpf_trace.c, when CONFIG_BPF_EVENTS is enabled.

Since the two are incompatible, there cannot be a shared declaration in a header file, but the lack of a prototype causes a W=1 warning:

kernel/bpf/core.c:1638:12: error: no previous prototype for 'bpf_probe_read_kernel' [-Werror=missing-prototypes]

On 32-bit architectures, the local prototype

u64 __weak bpf_probe_read_kernel(void *dst, u32 size, const void *unsafe_ptr)

passes arguments in other registers as the one in bpf_trace.c

BPF_CALL_3(bpf_probe_read_kernel, void *, dst, u32, size, const void *, unsafe_ptr)

which uses 64-bit arguments in pairs of registers.

Change the core.c file to only reference the inner bpf_probe_read_kernel_common() helper and provide a prototype for that, to ensure this is compatible with both definitions.

Cc: stable@vger.kernel.org Signed-off-by: Arnd Bergmann arnd@arndb.de

Sorry for the delay. I just took in patch 1/2, thanks!

Small comment below:

-- v3: clarify changelog text further. v2: rewrite completely to fix the mismatch.

---

include/linux/bpf.h | 2 ++ kernel/bpf/core.c | 9 ++++++--- kernel/trace/bpf_trace.c | 3 +-- 3 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h index f58895830adae..55826398acfba 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -2619,6 +2619,8 @@ static inline void bpf_dynptr_set_rdonly(struct bpf_dynptr_kern *ptr) } #endif /* CONFIG_BPF_SYSCALL */ +int bpf_probe_read_kernel_common(void *dst, u32 size, const void *unsafe_ptr);

• void __bpf_free_used_btfs(struct bpf_prog_aux *aux, struct btf_mod_pair *used_btfs, u32 len);

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 0926714641eb5..565ef6950c7a8 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -35,6 +35,7 @@ #include <linux/bpf_verifier.h> #include <linux/nodemask.h> #include <linux/nospec.h> +#include <linux/bpf.h> #include <linux/bpf_mem_alloc.h> #include <linux/memcontrol.h> @@ -1635,11 +1636,13 @@ bool bpf_opcode_in_insntable(u8 code) } #ifndef CONFIG_BPF_JIT_ALWAYS_ON -u64 __weak bpf_probe_read_kernel(void *dst, u32 size, const void *unsafe_ptr) +#ifndef CONFIG_BPF_EVENTS +int bpf_probe_read_kernel_common(void *dst, u32 size, const void *unsafe_ptr) { memset(dst, 0, size); return -EFAULT; } +#endif /**

• ___bpf_prog_run - run eBPF program on a given context

@@ -1931,8 +1934,8 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn) DST = *(SIZE *)(unsigned long) (SRC + insn->off); \ CONT; \ LDX_PROBE_MEM_##SIZEOP: \

• bpf_probe_read_kernel(&DST, sizeof(SIZE),		\
  

• 		      (const void *)(long) (SRC + insn->off));	\
  

• bpf_probe_read_kernel_common(&DST, sizeof(SIZE),	\
  

• 	      (const void *)(long) (SRC + insn->off));	\
  

  DST = *((SIZE *)&DST); \ CONT;

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 2bc41e6ac9fe0..290fdce2ce535 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -223,8 +223,7 @@ const struct bpf_func_proto bpf_probe_read_user_str_proto = { .arg3_type = ARG_ANYTHING, }; -static __always_inline int -bpf_probe_read_kernel_common(void *dst, u32 size, const void *unsafe_ptr) +int bpf_probe_read_kernel_common(void *dst, u32 size, const void *unsafe_ptr) { int ret;

Given this is critical fast-path, please find a solution where we don't need to penalize bpf_probe_read_kernel_common.

Thanks, Daniel