On Wed, 7 Aug 2019 at 08:44, Igor Lubashev <iluba...@akamai.com> wrote:
>
> Kernel is using CAP_SYSLOG capability instead of uid==0 and euid==0 when
> checking kptr_restrict. Make perf do the same.
>
> Also, the kernel is a more restrictive than "no restrictions" in case of
> kptr_restrict==0, so add the same logic to perf.
>
> Signed-off-by: Igor Lubashev <iluba...@akamai.com>
> ---
> tools/perf/util/symbol.c | 15 +++++++++++----
> 1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index 173f3378aaa0..046271103499 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -4,6 +4,7 @@
> #include <stdlib.h>
> #include <stdio.h>
> #include <string.h>
> +#include <linux/capability.h>
> #include <linux/kernel.h>
> #include <linux/mman.h>
> #include <linux/time64.h>
> @@ -15,8 +16,10 @@
> #include <inttypes.h>
> #include "annotate.h"
> #include "build-id.h"
> +#include "cap.h"
> #include "util.h"
> #include "debug.h"
> +#include "event.h"
> #include "machine.h"
> #include "map.h"
> #include "symbol.h"
> @@ -890,7 +893,11 @@ bool symbol__restricted_filename(const char *filename,
> {
> bool restricted = false;
>
> - if (symbol_conf.kptr_restrict) {
> + /* Per kernel/kallsyms.c:
> + * we also restrict when perf_event_paranoid > 1 w/o CAP_SYSLOG
> + */
> + if (symbol_conf.kptr_restrict ||
> + (perf_event_paranoid() > 1 && !perf_cap__capable(CAP_SYSLOG))) {
> char *r = realpath(filename, NULL);
>
# echo 0 > /proc/sys/kernel/kptr_restrict
# ./tools/perf/perf record -e instructions:k uname
perf: Segmentation fault
Obtained 10 stack frames.
./tools/perf/perf(sighandler_dump_stack+0x44) [0x55af9e5da5d4]
/lib/x86_64-linux-gnu/libc.so.6(+0x3ef20) [0x7fd31efb6f20]
./tools/perf/perf(perf_event__synthesize_kernel_mmap+0xa7) [0x55af9e590337]
./tools/perf/perf(+0x1cf5be) [0x55af9e50c5be]
./tools/perf/perf(cmd_record+0x1022) [0x55af9e50dff2]
./tools/perf/perf(+0x23f98d) [0x55af9e57c98d]
./tools/perf/perf(+0x23fc9e) [0x55af9e57cc9e]
./tools/perf/perf(main+0x369) [0x55af9e4f6bc9]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe7) [0x7fd31ef99b97]
./tools/perf/perf(_start+0x2a) [0x55af9e4f704a]
Segmentation fault
I can reproduce this on both x86 and ARM64.
> if (r != NULL) {
> @@ -2190,9 +2197,9 @@ static bool symbol__read_kptr_restrict(void)
> char line[8];
>
> if (fgets(line, sizeof(line), fp) != NULL)
> - value = ((geteuid() != 0) || (getuid() != 0)) ?
> - (atoi(line) != 0) :
> - (atoi(line) == 2);
> + value = perf_cap__capable(CAP_SYSLOG) ?
> + (atoi(line) >= 2) :
> + (atoi(line) != 0);
>
> fclose(fp);
> }
> --
> 2.7.4
>
