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Commit 7a2fb561 authored by Howard Chu's avatar Howard Chu Committed by Namhyung Kim
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perf trace: Fix iteration of syscall ids in syscalltbl->entries 

This is a bug found when implementing pretty-printing for the
landlock_add_rule system call, I decided to send this patch separately
because this is a serious bug that should be fixed fast.

I wrote a test program to do landlock_add_rule syscall in a loop,
yet perf trace -e landlock_add_rule freezes, giving no output.

This bug is introduced by the false understanding of the variable "key"
below:
```
for (key = 0; key < trace->sctbl->syscalls.nr_entries; ++key) {
	struct syscall *sc = trace__syscall_info(trace, NULL, key);
	...
}
```
The code above seems right at the beginning, but when looking at
syscalltbl.c, I found these lines:

```
for (i = 0; i <= syscalltbl_native_max_id; ++i)
	if (syscalltbl_native[i])
		++nr_entries;

entries = tbl->syscalls.entries = malloc(sizeof(struct syscall) * nr_entries);
...

for (i = 0, j = 0; i <= syscalltbl_native_max_id; ++i) {
	if (syscalltbl_native[i]) {
		entries[j].name = syscalltbl_native[i];
		entries[j].id = i;
		++j;
	}
}
```

meaning the key is merely an index to traverse the syscall table,
instead of the actual syscall id for this particular syscall.

So if one uses key to do trace__syscall_info(trace, NULL, key), because
key only goes up to trace->sctbl->syscalls.nr_entries, for example, on
my X86_64 machine, this number is 373, it will end up neglecting all
the rest of the syscall, in my case, everything after `rseq`, because
the traversal will stop at 373, and `rseq` is the last syscall whose id
is lower than 373

in tools/perf/arch/x86/include/generated/asm/syscalls_64.c:
```
	...
	[334] = "rseq",
	[424] = "pidfd_send_signal",
	...
```

The reason why the key is scrambled but perf trace works well is that
key is used in trace__syscall_info(trace, NULL, key) to do
trace->syscalls.table[id], this makes sure that the struct syscall returned
actually has an id the same value as key, making the later bpf_prog
matching all correct.

After fixing this bug, I can do perf trace on 38 more syscalls, and
because more syscalls are visible, we get 8 more syscalls that can be
augmented.

before:

perf $ perf trace -vv --max-events=1 |& grep Reusing
Reusing "open" BPF sys_enter augmenter for "stat"
Reusing "open" BPF sys_enter augmenter for "lstat"
Reusing "open" BPF sys_enter augmenter for "access"
Reusing "connect" BPF sys_enter augmenter for "accept"
Reusing "sendto" BPF sys_enter augmenter for "recvfrom"
Reusing "connect" BPF sys_enter augmenter for "bind"
Reusing "connect" BPF sys_enter augmenter for "getsockname"
Reusing "connect" BPF sys_enter augmenter for "getpeername"
Reusing "open" BPF sys_enter augmenter for "execve"
Reusing "open" BPF sys_enter augmenter for "truncate"
Reusing "open" BPF sys_enter augmenter for "chdir"
Reusing "open" BPF sys_enter augmenter for "mkdir"
Reusing "open" BPF sys_enter augmenter for "rmdir"
Reusing "open" BPF sys_enter augmenter for "creat"
Reusing "open" BPF sys_enter augmenter for "link"
Reusing "open" BPF sys_enter augmenter for "unlink"
Reusing "open" BPF sys_enter augmenter for "symlink"
Reusing "open" BPF sys_enter augmenter for "readlink"
Reusing "open" BPF sys_enter augmenter for "chmod"
Reusing "open" BPF sys_enter augmenter for "chown"
Reusing "open" BPF sys_enter augmenter for "lchown"
Reusing "open" BPF sys_enter augmenter for "mknod"
Reusing "open" BPF sys_enter augmenter for "statfs"
Reusing "open" BPF sys_enter augmenter for "pivot_root"
Reusing "open" BPF sys_enter augmenter for "chroot"
Reusing "open" BPF sys_enter augmenter for "acct"
Reusing "open" BPF sys_enter augmenter for "swapon"
Reusing "open" BPF sys_enter augmenter for "swapoff"
Reusing "open" BPF sys_enter augmenter for "delete_module"
Reusing "open" BPF sys_enter augmenter for "setxattr"
Reusing "open" BPF sys_enter augmenter for "lsetxattr"
Reusing "openat" BPF sys_enter augmenter for "fsetxattr"
Reusing "open" BPF sys_enter augmenter for "getxattr"
Reusing "open" BPF sys_enter augmenter for "lgetxattr"
Reusing "openat" BPF sys_enter augmenter for "fgetxattr"
Reusing "open" BPF sys_enter augmenter for "listxattr"
Reusing "open" BPF sys_enter augmenter for "llistxattr"
Reusing "open" BPF sys_enter augmenter for "removexattr"
Reusing "open" BPF sys_enter augmenter for "lremovexattr"
Reusing "fsetxattr" BPF sys_enter augmenter for "fremovexattr"
Reusing "open" BPF sys_enter augmenter for "mq_open"
Reusing "open" BPF sys_enter augmenter for "mq_unlink"
Reusing "fsetxattr" BPF sys_enter augmenter for "add_key"
Reusing "fremovexattr" BPF sys_enter augmenter for "request_key"
Reusing "fremovexattr" BPF sys_enter augmenter for "inotify_add_watch"
Reusing "fremovexattr" BPF sys_enter augmenter for "mkdirat"
Reusing "fremovexattr" BPF sys_enter augmenter for "mknodat"
Reusing "fremovexattr" BPF sys_enter augmenter for "fchownat"
Reusing "fremovexattr" BPF sys_enter augmenter for "futimesat"
Reusing "fremovexattr" BPF sys_enter augmenter for "newfstatat"
Reusing "fremovexattr" BPF sys_enter augmenter for "unlinkat"
Reusing "fremovexattr" BPF sys_enter augmenter for "linkat"
Reusing "open" BPF sys_enter augmenter for "symlinkat"
Reusing "fremovexattr" BPF sys_enter augmenter for "readlinkat"
Reusing "fremovexattr" BPF sys_enter augmenter for "fchmodat"
Reusing "fremovexattr" BPF sys_enter augmenter for "faccessat"
Reusing "fremovexattr" BPF sys_enter augmenter for "utimensat"
Reusing "connect" BPF sys_enter augmenter for "accept4"
Reusing "fremovexattr" BPF sys_enter augmenter for "name_to_handle_at"
Reusing "fremovexattr" BPF sys_enter augmenter for "renameat2"
Reusing "open" BPF sys_enter augmenter for "memfd_create"
Reusing "fremovexattr" BPF sys_enter augmenter for "execveat"
Reusing "fremovexattr" BPF sys_enter augmenter for "statx"

after

perf $ perf trace -vv --max-events=1 |& grep Reusing
Reusing "open" BPF sys_enter augmenter for "stat"
Reusing "open" BPF sys_enter augmenter for "lstat"
Reusing "open" BPF sys_enter augmenter for "access"
Reusing "connect" BPF sys_enter augmenter for "accept"
Reusing "sendto" BPF sys_enter augmenter for "recvfrom"
Reusing "connect" BPF sys_enter augmenter for "bind"
Reusing "connect" BPF sys_enter augmenter for "getsockname"
Reusing "connect" BPF sys_enter augmenter for "getpeername"
Reusing "open" BPF sys_enter augmenter for "execve"
Reusing "open" BPF sys_enter augmenter for "truncate"
Reusing "open" BPF sys_enter augmenter for "chdir"
Reusing "open" BPF sys_enter augmenter for "mkdir"
Reusing "open" BPF sys_enter augmenter for "rmdir"
Reusing "open" BPF sys_enter augmenter for "creat"
Reusing "open" BPF sys_enter augmenter for "link"
Reusing "open" BPF sys_enter augmenter for "unlink"
Reusing "open" BPF sys_enter augmenter for "symlink"
Reusing "open" BPF sys_enter augmenter for "readlink"
Reusing "open" BPF sys_enter augmenter for "chmod"
Reusing "open" BPF sys_enter augmenter for "chown"
Reusing "open" BPF sys_enter augmenter for "lchown"
Reusing "open" BPF sys_enter augmenter for "mknod"
Reusing "open" BPF sys_enter augmenter for "statfs"
Reusing "open" BPF sys_enter augmenter for "pivot_root"
Reusing "open" BPF sys_enter augmenter for "chroot"
Reusing "open" BPF sys_enter augmenter for "acct"
Reusing "open" BPF sys_enter augmenter for "swapon"
Reusing "open" BPF sys_enter augmenter for "swapoff"
Reusing "open" BPF sys_enter augmenter for "delete_module"
Reusing "open" BPF sys_enter augmenter for "setxattr"
Reusing "open" BPF sys_enter augmenter for "lsetxattr"
Reusing "openat" BPF sys_enter augmenter for "fsetxattr"
Reusing "open" BPF sys_enter augmenter for "getxattr"
Reusing "open" BPF sys_enter augmenter for "lgetxattr"
Reusing "openat" BPF sys_enter augmenter for "fgetxattr"
Reusing "open" BPF sys_enter augmenter for "listxattr"
Reusing "open" BPF sys_enter augmenter for "llistxattr"
Reusing "open" BPF sys_enter augmenter for "removexattr"
Reusing "open" BPF sys_enter augmenter for "lremovexattr"
Reusing "fsetxattr" BPF sys_enter augmenter for "fremovexattr"
Reusing "open" BPF sys_enter augmenter for "mq_open"
Reusing "open" BPF sys_enter augmenter for "mq_unlink"
Reusing "fsetxattr" BPF sys_enter augmenter for "add_key"
Reusing "fremovexattr" BPF sys_enter augmenter for "request_key"
Reusing "fremovexattr" BPF sys_enter augmenter for "inotify_add_watch"
Reusing "fremovexattr" BPF sys_enter augmenter for "mkdirat"
Reusing "fremovexattr" BPF sys_enter augmenter for "mknodat"
Reusing "fremovexattr" BPF sys_enter augmenter for "fchownat"
Reusing "fremovexattr" BPF sys_enter augmenter for "futimesat"
Reusing "fremovexattr" BPF sys_enter augmenter for "newfstatat"
Reusing "fremovexattr" BPF sys_enter augmenter for "unlinkat"
Reusing "fremovexattr" BPF sys_enter augmenter for "linkat"
Reusing "open" BPF sys_enter augmenter for "symlinkat"
Reusing "fremovexattr" BPF sys_enter augmenter for "readlinkat"
Reusing "fremovexattr" BPF sys_enter augmenter for "fchmodat"
Reusing "fremovexattr" BPF sys_enter augmenter for "faccessat"
Reusing "fremovexattr" BPF sys_enter augmenter for "utimensat"
Reusing "connect" BPF sys_enter augmenter for "accept4"
Reusing "fremovexattr" BPF sys_enter augmenter for "name_to_handle_at"
Reusing "fremovexattr" BPF sys_enter augmenter for "renameat2"
Reusing "open" BPF sys_enter augmenter for "memfd_create"
Reusing "fremovexattr" BPF sys_enter augmenter for "execveat"
Reusing "fremovexattr" BPF sys_enter augmenter for "statx"

TL;DR:

These are the new syscalls that can be augmented
Reusing "openat" BPF sys_enter augmenter for "open_tree"
Reusing "openat" BPF sys_enter augmenter for "openat2"
Reusing "openat" BPF sys_enter augmenter for "mount_setattr"
Reusing "openat" BPF sys_enter augmenter for "move_mount"
Reusing "open" BPF sys_enter augmenter for "fsopen"
Reusing "openat" BPF sys_enter augmenter for "fspick"
Reusing "openat" BPF sys_enter augmenter for "faccessat2"
Reusing "openat" BPF sys_enter augmenter for "fchmodat2"

as for the perf trace output:

before

perf $ perf trace -e faccessat2 --max-events=1
[no output]

after

perf $ ./perf trace -e faccessat2 --max-events=1
     0.000 ( 0.037 ms): waybar/958 faccessat2(dfd: 40, filename: "uevent")                               = 0

P.S. The reason why this bug was not found in the past five years is
probably because it only happens to the newer syscalls whose id is
greater, for instance, faccessat2 of id 439, which not a lot of people
care about when using perf trace.

[Arnaldo]: notes

That and the fact that the BPF code was hidden before having to use -e,
that got changed kinda recently when we switched to using BPF skels for
augmenting syscalls in 'perf trace':

⬢[acme@toolbox perf-tools-next]$ git log --oneline tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c
a9f4c6c9 perf trace: Collect sys_nanosleep first argument
29d16de2 perf augmented_raw_syscalls.bpf: Move 'struct timespec64' to vmlinux.h
5069211e perf trace: Use the right bpf_probe_read(_str) variant for reading user data
33b725ce perf trace: Avoid compile error wrt redefining bool
7d964231 perf bpf augmented_raw_syscalls: Add an assert to make sure sizeof(augmented_arg->value) is a power of two.
262b54b6 perf bpf augmented_raw_syscalls: Add an assert to make sure sizeof(saddr) is a power of two.
18364804 perf bpf_skel augmented_raw_syscalls: Cap the socklen parameter using &= sizeof(saddr)
cd2cece6 perf trace: Tidy comments related to BPF + syscall augmentation
5e6da6be perf trace: Migrate BPF augmentation to use a skeleton
⬢[acme@toolbox perf-tools-next]$

⬢[acme@toolbox perf-tools-next]$ git show --oneline --pretty=reference 5e6da6be | head -1
5e6da6be (perf trace: Migrate BPF augmentation to use a skeleton, 2023-08-10)
⬢[acme@toolbox perf-tools-next]$

I.e. from August, 2023.

One had as well to ask for BUILD_BPF_SKEL=1, which now is default if all
it needs is available on the system.

I simplified the code to not expose the 'struct syscall' outside of
tools/perf/util/syscalltbl.c, instead providing a function to go from
the index to the syscall id:

  int syscalltbl__id_at_idx(struct syscalltbl *tbl, int idx);
Signed-off-by: default avatarHoward Chu <howardchu95@gmail.com>
Tested-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
Link: https://lore.kernel.org/lkml/ZmhlAxbVcAKoPTg8@x1
Link: https://lore.kernel.org/r/20240705132059.853205-2-howardchu95@gmail.comSigned-off-by: default avatarNamhyung Kim <namhyung@kernel.org>
parent 1553419c
Hide whitespace changes
Inline Side-by-side
Showing with 15 additions and 7 deletions
tools/perf/builtin-trace.c
View file @ 7a2fb561
......@@ -3354,8 +3354,6 @@ static int trace__bpf_prog_sys_exit_fd(struct trace *trace, int id)
static struct bpf_program *trace__find_usable_bpf_prog_entry(struct trace *trace, struct syscall *sc)
{
struct tep_format_field *field, *candidate_field;
int id;
/*
* We're only interested in syscalls that have a pointer:
*/
......@@ -3367,7 +3365,8 @@ static struct bpf_program *trace__find_usable_bpf_prog_entry(struct trace *trace
return NULL;
try_to_find_pair:
for (id = 0; id < trace->sctbl->syscalls.nr_entries; ++id) {
for (int i = 0; i < trace->sctbl->syscalls.nr_entries; ++i) {
int id = syscalltbl__id_at_idx(trace->sctbl, i);
struct syscall *pair = trace__syscall_info(trace, NULL, id);
struct bpf_program *pair_prog;
bool is_candidate = false;
......@@ -3456,10 +3455,10 @@ static int trace__init_syscalls_bpf_prog_array_maps(struct trace *trace)
{
int map_enter_fd = bpf_map__fd(trace->skel->maps.syscalls_sys_enter);
int map_exit_fd = bpf_map__fd(trace->skel->maps.syscalls_sys_exit);
int err = 0, key;
int err = 0;
for (key = 0; key < trace->sctbl->syscalls.nr_entries; ++key) {
int prog_fd;
for (int i = 0; i < trace->sctbl->syscalls.nr_entries; ++i) {
int prog_fd, key = syscalltbl__id_at_idx(trace->sctbl, i);
if (!trace__syscall_enabled(trace, key))
continue;
......@@ -3505,7 +3504,8 @@ static int trace__init_syscalls_bpf_prog_array_maps(struct trace *trace)
* first and second arg (this one on the raw_syscalls:sys_exit prog
* array tail call, then that one will be used.
*/
for (key = 0; key < trace->sctbl->syscalls.nr_entries; ++key) {
for (int i = 0; i < trace->sctbl->syscalls.nr_entries; ++i) {
int key = syscalltbl__id_at_idx(trace->sctbl, i);
struct syscall *sc = trace__syscall_info(trace, NULL, key);
struct bpf_program *pair_prog;
int prog_fd;
......
tools/perf/util/syscalltbl.c
View file @ 7a2fb561
......@@ -123,6 +123,13 @@ int syscalltbl__id(struct syscalltbl *tbl, const char *name)
return sc ? sc->id : -1;
}
int syscalltbl__id_at_idx(struct syscalltbl *tbl, int idx)
{
struct syscall *syscalls = tbl->syscalls.entries;
return idx < tbl->syscalls.nr_entries ? syscalls[idx].id : -1;
}
int syscalltbl__strglobmatch_next(struct syscalltbl *tbl, const char *syscall_glob, int *idx)
{
int i;
......
tools/perf/util/syscalltbl.h
View file @ 7a2fb561
......@@ -16,6 +16,7 @@ void syscalltbl__delete(struct syscalltbl *tbl);
const char *syscalltbl__name(const struct syscalltbl *tbl, int id);
int syscalltbl__id(struct syscalltbl *tbl, const char *name);
int syscalltbl__id_at_idx(struct syscalltbl *tbl, int idx);
int syscalltbl__strglobmatch_first(struct syscalltbl *tbl, const char *syscall_glob, int *idx);
int syscalltbl__strglobmatch_next(struct syscalltbl *tbl, const char *syscall_glob, int *idx);
......
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