Hi Vincent!
On Thu, 7 Nov 2019 10:51:05 +0000
vincent.donnefort@xxxxxxx wrote:
> From: Vincent Donnefort <vincent.donnefort@xxxxxxx>
>
> kptr_restrict might prevent trace-cmd from accessing /proc/kallsyms,
> leading to a trace without the kernel function names resolved.
>
> Signed-off-by: Vincent Donnefort <vincent.donnefort@xxxxxxx>
>
> diff --git a/lib/trace-cmd/trace-output.c b/lib/trace-cmd/trace-output.c
> index 41932ee..3c4f306 100644
> --- a/lib/trace-cmd/trace-output.c
> +++ b/lib/trace-cmd/trace-output.c
> @@ -674,6 +674,39 @@ static int read_event_files(struct tracecmd_output *handle,
> return ret;
> }
>
> +static void set_proc_kptr_restrict(int reset)
> +{
> + char *path = "/proc/sys/kernel/kptr_restrict";
I believe this is a relatively new file. We should do a stat to see if
it exists, and if it does not, simply fail silently. I don't think we
want to give a warning if the file doesn't exist because the kernel
doesn't have it.
> + static char saved = 'X';
> + int fd, ret = -1;
> + char buf;
> +
> + fd = open(path, O_RDONLY);
> + if (fd < 0)
> + goto err;
> +
> + if (reset) {
> + buf = saved;
> + } else {
> + if (read(fd, &buf, 1) < 0)
> + goto err;
> + saved = buf;
> + buf = '0';
> + }
> + close(fd);
> +
Perhaps if reset is true and buf == 'X', we should simply exit, as it
would appear that we never put anything into buf. And probably should
make the 'X' a macro:
#define KPTR_UNINITIALIZED 'X'
static char saved = KPTR_UNINITIALIZED;
[..]
if (reset && buf == KPTR_UNINITIALIZED)
return;
-- Steve
> + fd = open(path, O_WRONLY);
> + if (fd < 0)
> + goto err;
> + if (write(fd, &buf, 1) > 0)
> + ret = 0;
> +err:
> + if (fd > 0)
> + close(fd);
> + if (ret)
> + warning("can't set kptr_restrict");
> +}
> +
> static int read_proc_kallsyms(struct tracecmd_output *handle,
> const char *kallsyms)
> {
> @@ -698,12 +731,16 @@ static int read_proc_kallsyms(struct tracecmd_output *handle,
> endian4 = convert_endian_4(handle, size);
> if (do_write_check(handle, &endian4, 4))
> return -1;
> +
> + set_proc_kptr_restrict(0);
> check_size = copy_file(handle, path);
> if (size != check_size) {
> errno = EINVAL;
> warning("error in size of file '%s'", path);
> + set_proc_kptr_restrict(1);
> return -1;
> }
> + set_proc_kptr_restrict(1);
>
> return 0;
> }
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