Re: [PATCH bpf-next 2/3] bpf: emit RECORD_MMAP events for bpf prog load/unload

[Alexei Starovoitov]

On 9/19/18 4:44 PM, Song Liu wrote:

On Sep 19, 2018, at 3:39 PM, Alexei Starovoitov <a...@kernel.org> wrote:

use perf_event_mmap_bpf_prog() helper to notify user space
about JITed bpf programs.
Use RECORD_MMAP perf event to tell user space where JITed bpf program was 
loaded.
Use empty program name as unload indication.

Signed-off-by: Alexei Starovoitov <a...@kernel.org>
---
kernel/bpf/core.c | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 3f5bf1af0826..ddf11fdafd36 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -384,7 +384,7 @@ bpf_get_prog_addr_region(const struct bpf_prog *prog,
        *symbol_end   = addr + hdr->pages * PAGE_SIZE;
}

-static void bpf_get_prog_name(const struct bpf_prog *prog, char *sym)
+static char *bpf_get_prog_name(const struct bpf_prog *prog, char *sym)
{
        const char *end = sym + KSYM_NAME_LEN;

@@ -402,9 +402,10 @@ static void bpf_get_prog_name(const struct bpf_prog *prog, 
char *sym)
        sym += snprintf(sym, KSYM_NAME_LEN, "bpf_prog_");
        sym  = bin2hex(sym, prog->tag, sizeof(prog->tag));
        if (prog->aux->name[0])
-               snprintf(sym, (size_t)(end - sym), "_%s", prog->aux->name);
+               sym += snprintf(sym, (size_t)(end - sym), "_%s", 
prog->aux->name);
        else
                *sym = 0;
+       return sym;
}

static __always_inline unsigned long
@@ -480,23 +481,40 @@ static bool bpf_prog_kallsyms_verify_off(const struct 
bpf_prog *fp)

void bpf_prog_kallsyms_add(struct bpf_prog *fp)
{
+       unsigned long symbol_start, symbol_end;
+       char buf[KSYM_NAME_LEN], *sym;
+
        if (!bpf_prog_kallsyms_candidate(fp) ||
            !capable(CAP_SYS_ADMIN))
                return;

+       bpf_get_prog_addr_region(fp, &symbol_start, &symbol_end);
+       sym = bpf_get_prog_name(fp, buf);
+       sym++; /* sym - buf is the length of the name including trailing 0 */
+       while (!IS_ALIGNED(sym - buf, sizeof(u64)))
+               *sym++ = 0;

nit: This logic feels a little weird to me. How about we wrap the extra logic
in a separate function:

size_t bpf_get_prog_name_u64_aligned(const struct bpf_prog fp, char *buf)

probably bpf_get_prog_name_u64_padded() ?
would be cleaner indeed.

Will send v2 once Peter and Arnaldo provide their feedback.

Thanks for reviewing!