[PATCH 1/2] tracing: Do not let histogram values have some modifiers

Steven Rostedt
2023-03-02T02:08:23Z

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

Histogram values can not be strings, stacktraces, graphs, symbols,
syscalls, or grouped in buckets or log. Give an error if a value is set to
do so.

Note, the histogram code was not prepared to handle these modifiers for
histograms and caused a bug.

Mark Rutland reported:

# echo 'p:copy_to_user __arch_copy_to_user n=$arg2' >> /sys/kernel/tracing/kprobe_events
# echo 'hist:keys=n:vals=hitcount.buckets=8:sort=hitcount' > /sys/kernel/tracing/events/kprobes/copy_to_user/trigger
# cat /sys/kernel/tracing/events/kprobes/copy_to_user/hist
[ 143.694628] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
[ 143.695190] Mem abort info:
[ 143.695362] ESR = 0x0000000096000004
[ 143.695604] EC = 0x25: DABT (current EL), IL = 32 bits
[ 143.695889] SET = 0, FnV = 0
[ 143.696077] EA = 0, S1PTW = 0
[ 143.696302] FSC = 0x04: level 0 translation fault
[ 143.702381] Data abort info:
[ 143.702614] ISV = 0, ISS = 0x00000004
[ 143.702832] CM = 0, WnR = 0
[ 143.703087] user pgtable: 4k pages, 48-bit VAs, pgdp=00000000448f9000
[ 143.703407] [0000000000000000] pgd=0000000000000000, p4d=0000000000000000
[ 143.704137] Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP
[ 143.704714] Modules linked in:
[ 143.705273] CPU: 0 PID: 133 Comm: cat Not tainted 6.2.0-00003-g6fc512c10a7c #3
[ 143.706138] Hardware name: linux,dummy-virt (DT)
[ 143.706723] pstate: 80000005 (Nzcv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 143.707120] pc : hist_field_name.part.0+0x14/0x140
[ 143.707504] lr : hist_field_name.part.0+0x104/0x140
[ 143.707774] sp : ffff800008333a30
[ 143.707952] x29: ffff800008333a30 x28: 0000000000000001 x27: 0000000000400cc0
[ 143.708429] x26: ffffd7a653b20260 x25: 0000000000000000 x24: ffff10d303ee5800
[ 143.708776] x23: ffffd7a6539b27b0 x22: ffff10d303fb8c00 x21: 0000000000000001
[ 143.709127] x20: ffff10d303ec2000 x19: 0000000000000000 x18: 0000000000000000
[ 143.709478] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
[ 143.709824] x14: 0000000000000000 x13: 203a6f666e692072 x12: 6567676972742023
[ 143.710179] x11: 0a230a6d6172676f x10: 000000000000002c x9 : ffffd7a6521e018c
[ 143.710584] x8 : 000000000000002c x7 : 7f7f7f7f7f7f7f7f x6 : 000000000000002c
[ 143.710915] x5 : ffff10d303b0103e x4 : ffffd7a653b20261 x3 : 000000000000003d
[ 143.711239] x2 : 0000000000020001 x1 : 0000000000000001 x0 : 0000000000000000
[ 143.711746] Call trace:
[ 143.712115] hist_field_name.part.0+0x14/0x140
[ 143.712642] hist_field_name.part.0+0x104/0x140
[ 143.712925] hist_field_print+0x28/0x140
[ 143.713125] event_hist_trigger_print+0x174/0x4d0
[ 143.713348] hist_show+0xf8/0x980
[ 143.713521] seq_read_iter+0x1bc/0x4b0
[ 143.713711] seq_read+0x8c/0xc4
[ 143.713876] vfs_read+0xc8/0x2a4
[ 143.714043] ksys_read+0x70/0xfc
[ 143.714218] __arm64_sys_read+0x24/0x30
[ 143.714400] invoke_syscall+0x50/0x120
[ 143.714587] el0_svc_common.constprop.0+0x4c/0x100
[ 143.714807] do_el0_svc+0x44/0xd0
[ 143.714970] el0_svc+0x2c/0x84
[ 143.715134] el0t_64_sync_handler+0xbc/0x140
[ 143.715334] el0t_64_sync+0x190/0x194
[ 143.715742] Code: a9bd7bfd 910003fd a90153f3 aa0003f3 (f9400000)
[ 143.716510] ---[ end trace 0000000000000000 ]---
Segmentation fault

Cc: stable@vger.kernel.org
Fixes: c6afad49d127f ("tracing: Add hist trigger 'sym' and 'sym-offset' modifiers")
Reported-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
kernel/trace/trace_events_hist.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 89877a18f933..6e8ab726a7b5 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -4235,6 +4235,15 @@ static int __create_val_field(struct hist_trigger_data *hist_data,
goto out;
}

+ /* Some types cannot be a value */
+ if (hist_field->flags & (HIST_FIELD_FL_GRAPH | HIST_FIELD_FL_PERCENT |
+ HIST_FIELD_FL_BUCKET | HIST_FIELD_FL_LOG2 |
+ HIST_FIELD_FL_SYM | HIST_FIELD_FL_SYM_OFFSET |
+ HIST_FIELD_FL_SYSCALL | HIST_FIELD_FL_STACKTRACE)) {
+ hist_err(file->tr, HIST_ERR_BAD_FIELD_MODIFIER, errpos(field_str));
+ ret = -EINVAL;
+ }
+
hist_data->fields[val_idx] = hist_field;

++hist_data->n_vals;
--
2.39.1