bpf: fix bpf_probe_read_kernel prototype mismatch

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.

As both versions of the function are fairly simple and only really
differ in one line, just move them into a header file as an inline
function that does not add any overhead for the bpf_trace.c callers
and actually avoids a function call for the other one.

Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/ac25cb0f-b804-1649-3afb-1dc6138c2716@iogearbox.net/
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20230801111449.185301-1-arnd@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index ceaa8c2..abe7506 100644 (file)
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2661,6 +2661,18 @@ static inline void bpf_dynptr_set_rdonly(struct bpf_dynptr_kern *ptr)
 }
 #endif /* CONFIG_BPF_SYSCALL */
 
+static __always_inline int
+bpf_probe_read_kernel_common(void *dst, u32 size, const void *unsafe_ptr)
+{
+       int ret = -EFAULT;
+
+       if (IS_ENABLED(CONFIG_BPF_EVENTS))
+               ret = copy_from_kernel_nofault(dst, unsafe_ptr, size);
+       if (unlikely(ret < 0))
+               memset(dst, 0, size);
+       return ret;
+}
+
 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 baccdec..0f8f036 100644 (file)
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1650,12 +1650,6 @@ 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)
-{
-       memset(dst, 0, size);
-       return -EFAULT;
-}
-
 /**
  *     ___bpf_prog_run - run eBPF program on a given context
  *     @regs: is the array of MAX_BPF_EXT_REG eBPF pseudo-registers
@@ -2066,8 +2060,8 @@ out:
                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;
 
@@ -2082,7 +2076,7 @@ out:
                DST = *(SIZE *)(unsigned long) (SRC + insn->off);       \
                CONT;                                                   \
        LDX_PROBE_MEMSX_##SIZEOP:                                       \
-               bpf_probe_read_kernel(&DST, sizeof(SIZE),               \
+               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 c92eb8c..83bde24 100644 (file)
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -223,17 +223,6 @@ 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 ret;
-
-       ret = copy_from_kernel_nofault(dst, unsafe_ptr, size);
-       if (unlikely(ret < 0))
-               memset(dst, 0, size);
-       return ret;
-}
-
 BPF_CALL_3(bpf_probe_read_kernel, void *, dst, u32, size,
           const void *, unsafe_ptr)
 {