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perf trace: Factor out BPF loop body

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The BPF program in augmented_raw_syscalls uses a for loop to iterate all
syscall arguments. The loop body is quite complex and often poses
problems for the BPF verifier. As a preparation step for addressing this
issue, factor out the loop body into a separate function.

Signed-off-by: Viktor Malik <vmalik@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
This commit is contained in:
Viktor Malik 2026-07-07 08:52:46 +02:00 committed by Namhyung Kim
parent c341749d6a
commit acff3e1a9c
1 changed files with 73 additions and 55 deletions
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128
tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c
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@ -429,15 +429,80 @@ static bool pid_filter__has(struct pids_filtered *pids, pid_t pid)
return bpf_map_lookup_elem(pids, &pid) != NULL;
}
/*
* Determine what type of argument and how many bytes to read from user space, using the
* value in the beauty_map. This is the relation of parameter type and its corresponding
* value in the beauty map, and how many bytes we read eventually:
*
* string: 1 -> size of string
* struct: size of struct -> size of struct
* buffer: -1 * (index of paired len) -> value of paired len (maximum: TRACE_AUG_MAX_BUF)
*/
static inline int augment_arg(struct syscall_enter_args *args, int i,
unsigned int *beauty_map,
struct augmented_arg *payload_offset)
{
int index, value_size = sizeof(struct augmented_arg) - offsetof(struct augmented_arg, value);
s64 aug_size, size;
bool augmented;
void *arg;
arg = (void *)args->args[i];
augmented = false;
size = beauty_map[i];
aug_size = size; /* size of the augmented data read from user space */
if (size == 0 || arg == NULL)
return 0;
if (size == 1) { /* string */
aug_size = bpf_probe_read_user_str(payload_offset->value, value_size, arg);
/* minimum of 0 to pass the verifier */
if (aug_size < 0)
aug_size = 0;
augmented = true;
} else if (size > 0 && size <= value_size) { /* struct */
if (!bpf_probe_read_user(payload_offset->value, size, arg))
augmented = true;
} else if ((int)size < 0 && size >= -6) { /* buffer */
index = -(size + 1);
barrier_var(index); // Prevent clang (noticed with v18) from removing the &= 7 trick.
index &= 7; // Satisfy the bounds checking with the verifier in some kernels.
aug_size = args->args[index] > TRACE_AUG_MAX_BUF ? TRACE_AUG_MAX_BUF : args->args[index];
if (aug_size > 0) {
if (!bpf_probe_read_user(payload_offset->value, aug_size, arg))
augmented = true;
}
}
/* Augmented data size is limited to sizeof(augmented_arg->unnamed union with value field) */
if (aug_size > value_size)
aug_size = value_size;
/* write data to payload */
if (augmented) {
int written = offsetof(struct augmented_arg, value) + aug_size;
if (written < 0 || written > sizeof(struct augmented_arg))
return -1;
payload_offset->size = aug_size;
return written;
}
return 0;
}
static int augment_sys_enter(void *ctx, struct syscall_enter_args *args)
{
bool augmented, do_output = false;
int zero = 0, index, value_size = sizeof(struct augmented_arg) - offsetof(struct augmented_arg, value);
bool do_output = false;
int zero = 0, written;
u64 output = 0; /* has to be u64, otherwise it won't pass the verifier */
s64 aug_size, size;
unsigned int nr, *beauty_map;
struct beauty_payload_enter *payload;
void *arg, *payload_offset;
void *payload_offset;
/* fall back to do predefined tail call */
if (args == NULL)
@ -457,58 +522,11 @@ static int augment_sys_enter(void *ctx, struct syscall_enter_args *args)
/* copy the sys_enter header, which has the syscall_nr */
__builtin_memcpy(&payload->args, args, sizeof(struct syscall_enter_args));
/*
* Determine what type of argument and how many bytes to read from user space, using the
* value in the beauty_map. This is the relation of parameter type and its corresponding
* value in the beauty map, and how many bytes we read eventually:
*
* string: 1 -> size of string
* struct: size of struct -> size of struct
* buffer: -1 * (index of paired len) -> value of paired len (maximum: TRACE_AUG_MAX_BUF)
*/
for (int i = 0; i < 6; i++) {
arg = (void *)args->args[i];
augmented = false;
size = beauty_map[i];
aug_size = size; /* size of the augmented data read from user space */
if (size == 0 || arg == NULL)
continue;
if (size == 1) { /* string */
aug_size = bpf_probe_read_user_str(((struct augmented_arg *)payload_offset)->value, value_size, arg);
/* minimum of 0 to pass the verifier */
if (aug_size < 0)
aug_size = 0;
augmented = true;
} else if (size > 0 && size <= value_size) { /* struct */
if (!bpf_probe_read_user(((struct augmented_arg *)payload_offset)->value, size, arg))
augmented = true;
} else if ((int)size < 0 && size >= -6) { /* buffer */
index = -(size + 1);
barrier_var(index); // Prevent clang (noticed with v18) from removing the &= 7 trick.
index &= 7; // Satisfy the bounds checking with the verifier in some kernels.
aug_size = args->args[index] > TRACE_AUG_MAX_BUF ? TRACE_AUG_MAX_BUF : args->args[index];
if (aug_size > 0) {
if (!bpf_probe_read_user(((struct augmented_arg *)payload_offset)->value, aug_size, arg))
augmented = true;
}
}
/* Augmented data size is limited to sizeof(augmented_arg->unnamed union with value field) */
if (aug_size > value_size)
aug_size = value_size;
/* write data to payload */
if (augmented) {
int written = offsetof(struct augmented_arg, value) + aug_size;
if (written < 0 || written > sizeof(struct augmented_arg))
return 1;
((struct augmented_arg *)payload_offset)->size = aug_size;
written = augment_arg(args, i, beauty_map, (struct augmented_arg *)payload_offset);
if (written < 0)
return 1;
if (written > 0) {
output += written;
payload_offset += written;
do_output = true;