[PATCH bpf-next v7 1/3] bpf: refactor max_depth computation in bpf_get_stack()

[PATCH bpf-next v7 1/3] bpf: refactor max_depth computation in bpf_get_stack()

[Arnaud Lecomte]

A new helper function stack_map_calculate_max_depth() that
computes the max depth for a stackmap.

Changes in v2:
 - Removed the checking 'map_size % map_elem_size' from
   stack_map_calculate_max_depth
 - Changed stack_map_calculate_max_depth params name to be more generic

Changes in v3:
 - Changed map size param to size in max depth helper

Changes in v4:
 - Fixed indentation in max depth helper for args

Changes in v5:
 - Bound back trace_nr to num_elem in __bpf_get_stack
 - Make a copy of sysctl_perf_event_max_stack
   in stack_map_calculate_max_depth

Changes in v6:
 - Restrained max_depth computation only when required
 - Additional cleanup from Song in __bpf_get_stack

Changes in v7:
 - Removed additional cleanup from v6

Link to v6: https://lore.kernel.org/all/20250903135323.97847-1-contact@arnaud-lcm.com/

Signed-off-by: Arnaud Lecomte <contact@arnaud-lcm.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
---
 kernel/bpf/stackmap.c | 38 +++++++++++++++++++++++++++-----------
 1 file changed, 27 insertions(+), 11 deletions(-)

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index 3615c06b7dfa..ed707bc07173 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -42,6 +42,28 @@ static inline int stack_map_data_size(struct bpf_map *map)
 		sizeof(struct bpf_stack_build_id) : sizeof(u64);
 }
 
+/**
+ * stack_map_calculate_max_depth - Calculate maximum allowed stack trace depth
+ * @size:  Size of the buffer/map value in bytes
+ * @elem_size:  Size of each stack trace element
+ * @flags:  BPF stack trace flags (BPF_F_USER_STACK, BPF_F_USER_BUILD_ID, ...)
+ *
+ * Return: Maximum number of stack trace entries that can be safely stored
+ */
+static u32 stack_map_calculate_max_depth(u32 size, u32 elem_size, u64 flags)
+{
+	u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
+	u32 max_depth;
+	u32 curr_sysctl_max_stack = READ_ONCE(sysctl_perf_event_max_stack);
+
+	max_depth = size / elem_size;
+	max_depth += skip;
+	if (max_depth > curr_sysctl_max_stack)
+		return curr_sysctl_max_stack;
+
+	return max_depth;
+}
+
 static int prealloc_elems_and_freelist(struct bpf_stack_map *smap)
 {
 	u64 elem_size = sizeof(struct stack_map_bucket) +
@@ -300,20 +322,17 @@ static long __bpf_get_stackid(struct bpf_map *map,
 BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
 	   u64, flags)
 {
-	u32 max_depth = map->value_size / stack_map_data_size(map);
-	u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
+	u32 elem_size = stack_map_data_size(map);
 	bool user = flags & BPF_F_USER_STACK;
 	struct perf_callchain_entry *trace;
 	bool kernel = !user;
+	u32 max_depth;
 
 	if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
 			       BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID)))
 		return -EINVAL;
 
-	max_depth += skip;
-	if (max_depth > sysctl_perf_event_max_stack)
-		max_depth = sysctl_perf_event_max_stack;
-
+	max_depth = stack_map_calculate_max_depth(map->value_size, elem_size, flags);
 	trace = get_perf_callchain(regs, 0, kernel, user, max_depth,
 				   false, false);
 
@@ -406,8 +425,8 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
 			    struct perf_callchain_entry *trace_in,
 			    void *buf, u32 size, u64 flags, bool may_fault)
 {
-	u32 trace_nr, copy_len, elem_size, num_elem, max_depth;
 	bool user_build_id = flags & BPF_F_USER_BUILD_ID;
+	u32 trace_nr, copy_len, elem_size, max_depth;
 	bool crosstask = task && task != current;
 	u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
 	bool user = flags & BPF_F_USER_STACK;
@@ -438,10 +457,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
 		goto clear;
 	}
 
-	num_elem = size / elem_size;
-	max_depth = num_elem + skip;
-	if (sysctl_perf_event_max_stack < max_depth)
-		max_depth = sysctl_perf_event_max_stack;
+	max_depth = stack_map_calculate_max_depth(size, elem_size, flags);
 
 	if (may_fault)
 		rcu_read_lock(); /* need RCU for perf's callchain below */
-- 
2.47.3

[PATCH bpf-next v7 2/3] bpf: clean-up bounds checking in __bpf_get_stack

[Arnaud Lecomte]

Clean-up bounds checking for trace->nr in
__bpf_get_stack by limiting it only to
max_depth.

Signed-off-by: Arnaud Lecomte <contact@arnaud-lcm.com>
Cc: Song Lui <song@kernel.org>
---
 kernel/bpf/stackmap.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index ed707bc07173..9f3ae426ddc3 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -462,13 +462,15 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
 	if (may_fault)
 		rcu_read_lock(); /* need RCU for perf's callchain below */
 
-	if (trace_in)
+	if (trace_in) {
 		trace = trace_in;
-	else if (kernel && task)
+		trace->nr = min_t(u32, trace->nr, max_depth);
+	} else if (kernel && task) {
 		trace = get_callchain_entry_for_task(task, max_depth);
-	else
+	} else {
 		trace = get_perf_callchain(regs, 0, kernel, user, max_depth,
 					   crosstask, false);
+	}
 
 	if (unlikely(!trace) || trace->nr < skip) {
 		if (may_fault)
@@ -477,7 +479,6 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
 	}
 
 	trace_nr = trace->nr - skip;
-	trace_nr = (trace_nr <= num_elem) ? trace_nr : num_elem;
 	copy_len = trace_nr * elem_size;
 
 	ips = trace->ip + skip;
-- 
2.47.3

[PATCH bpf-next v7 3/3] bpf: fix stackmap overflow check in __bpf_get_stackid()

[Arnaud Lecomte]

Syzkaller reported a KASAN slab-out-of-bounds write in __bpf_get_stackid()
when copying stack trace data. The issue occurs when the perf trace
 contains more stack entries than the stack map bucket can hold,
 leading to an out-of-bounds write in the bucket's data array.

Changes in v2:
 - Fixed max_depth names across get stack id

Changes in v4:
 - Removed unnecessary empty line in __bpf_get_stackid

Changs in v6:
 - Added back trace_len computation in __bpf_get_stackid

Link to v6: https://lore.kernel.org/all/20250903135348.97884-1-contact@arnaud-lcm.com/

Reported-by: syzbot+c9b724fbb41cf2538b7b@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c9b724fbb41cf2538b7b
Fixes: ee2a098851bf ("bpf: Adjust BPF stack helper functions to accommodate skip > 0")
Signed-off-by: Arnaud Lecomte <contact@arnaud-lcm.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
---
 kernel/bpf/stackmap.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index 9f3ae426ddc3..29e05c9ff1bd 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -369,6 +369,7 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,
 {
 	struct perf_event *event = ctx->event;
 	struct perf_callchain_entry *trace;
+	u32 elem_size, max_depth;
 	bool kernel, user;
 	__u64 nr_kernel;
 	int ret;
@@ -390,11 +391,15 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,
 		return -EFAULT;
 
 	nr_kernel = count_kernel_ip(trace);
+	elem_size = stack_map_data_size(map);
 
 	if (kernel) {
 		__u64 nr = trace->nr;
 
 		trace->nr = nr_kernel;
+		max_depth =
+			stack_map_calculate_max_depth(map->value_size, elem_size, flags);
+		trace->nr = min_t(u32, nr_kernel, max_depth);
 		ret = __bpf_get_stackid(map, trace, flags);
 
 		/* restore nr */
@@ -407,6 +412,9 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,
 			return -EFAULT;
 
 		flags = (flags & ~BPF_F_SKIP_FIELD_MASK) | skip;
+		max_depth =
+			stack_map_calculate_max_depth(map->value_size, elem_size, flags);
+		trace->nr = min_t(u32, trace->nr, max_depth);
 		ret = __bpf_get_stackid(map, trace, flags);
 	}
 	return ret;
-- 
2.47.3

Re: [PATCH bpf-next v7 2/3] bpf: clean-up bounds checking in __bpf_get_stack

[Song Liu]

On 9/3/25 4:40 PM, Arnaud Lecomte wrote:
> Clean-up bounds checking for trace->nr in
> __bpf_get_stack by limiting it only to
> max_depth.
>
> Signed-off-by: Arnaud Lecomte <contact@arnaud-lcm.com>
> Cc: Song Lui <song@kernel.org>

Typo in my name, which is "Song Liu".

This looks right.

Acked-by: Song Liu <song@kernel.org>

> ---
>   kernel/bpf/stackmap.c | 9 +++++----
>   1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
> index ed707bc07173..9f3ae426ddc3 100644
> --- a/kernel/bpf/stackmap.c
> +++ b/kernel/bpf/stackmap.c
> @@ -462,13 +462,15 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
>   	if (may_fault)
>   		rcu_read_lock(); /* need RCU for perf's callchain below */
>   
> -	if (trace_in)
> +	if (trace_in) {
>   		trace = trace_in;
> -	else if (kernel && task)
> +		trace->nr = min_t(u32, trace->nr, max_depth);
> +	} else if (kernel && task) {
>   		trace = get_callchain_entry_for_task(task, max_depth);
> -	else
> +	} else {
>   		trace = get_perf_callchain(regs, 0, kernel, user, max_depth,
>   					   crosstask, false);
> +	}
>   
>   	if (unlikely(!trace) || trace->nr < skip) {
>   		if (may_fault)
> @@ -477,7 +479,6 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
>   	}
>   
>   	trace_nr = trace->nr - skip;
> -	trace_nr = (trace_nr <= num_elem) ? trace_nr : num_elem;
>   	copy_len = trace_nr * elem_size;
>   
>   	ips = trace->ip + skip;

Re: [PATCH bpf-next v7 1/3] bpf: refactor max_depth computation in bpf_get_stack()

[Song Liu]

On 9/3/25 4:39 PM, Arnaud Lecomte wrote:
> A new helper function stack_map_calculate_max_depth() that
> computes the max depth for a stackmap.
>
> Changes in v2:
>   - Removed the checking 'map_size % map_elem_size' from
>     stack_map_calculate_max_depth
>   - Changed stack_map_calculate_max_depth params name to be more generic
>
> Changes in v3:
>   - Changed map size param to size in max depth helper
>
> Changes in v4:
>   - Fixed indentation in max depth helper for args
>
> Changes in v5:
>   - Bound back trace_nr to num_elem in __bpf_get_stack
>   - Make a copy of sysctl_perf_event_max_stack
>     in stack_map_calculate_max_depth
>
> Changes in v6:
>   - Restrained max_depth computation only when required
>   - Additional cleanup from Song in __bpf_get_stack
>
> Changes in v7:
>   - Removed additional cleanup from v6
>
> Link to v6: https://lore.kernel.org/all/20250903135323.97847-1-contact@arnaud-lcm.com/
>
> Signed-off-by: Arnaud Lecomte <contact@arnaud-lcm.com>
> Acked-by: Yonghong Song <yonghong.song@linux.dev>

Acked-by: Song Liu <song@kernel.org>


> ---
>   kernel/bpf/stackmap.c | 38 +++++++++++++++++++++++++++-----------
>   1 file changed, 27 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
> index 3615c06b7dfa..ed707bc07173 100644
> --- a/kernel/bpf/stackmap.c
> +++ b/kernel/bpf/stackmap.c
> @@ -42,6 +42,28 @@ static inline int stack_map_data_size(struct bpf_map *map)
>   		sizeof(struct bpf_stack_build_id) : sizeof(u64);
>   }
>   
> +/**
> + * stack_map_calculate_max_depth - Calculate maximum allowed stack trace depth
> + * @size:  Size of the buffer/map value in bytes
> + * @elem_size:  Size of each stack trace element
> + * @flags:  BPF stack trace flags (BPF_F_USER_STACK, BPF_F_USER_BUILD_ID, ...)
> + *
> + * Return: Maximum number of stack trace entries that can be safely stored
> + */
> +static u32 stack_map_calculate_max_depth(u32 size, u32 elem_size, u64 flags)
> +{
> +	u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
> +	u32 max_depth;
> +	u32 curr_sysctl_max_stack = READ_ONCE(sysctl_perf_event_max_stack);
> +
> +	max_depth = size / elem_size;
> +	max_depth += skip;
> +	if (max_depth > curr_sysctl_max_stack)
> +		return curr_sysctl_max_stack;
> +
> +	return max_depth;
> +}
> +
>   static int prealloc_elems_and_freelist(struct bpf_stack_map *smap)
>   {
>   	u64 elem_size = sizeof(struct stack_map_bucket) +
> @@ -300,20 +322,17 @@ static long __bpf_get_stackid(struct bpf_map *map,
>   BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
>   	   u64, flags)
>   {
> -	u32 max_depth = map->value_size / stack_map_data_size(map);
> -	u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
> +	u32 elem_size = stack_map_data_size(map);
>   	bool user = flags & BPF_F_USER_STACK;
>   	struct perf_callchain_entry *trace;
>   	bool kernel = !user;
> +	u32 max_depth;
>   
>   	if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
>   			       BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID)))
>   		return -EINVAL;
>   
> -	max_depth += skip;
> -	if (max_depth > sysctl_perf_event_max_stack)
> -		max_depth = sysctl_perf_event_max_stack;
> -
> +	max_depth = stack_map_calculate_max_depth(map->value_size, elem_size, flags);
>   	trace = get_perf_callchain(regs, 0, kernel, user, max_depth,
>   				   false, false);
>   
> @@ -406,8 +425,8 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
>   			    struct perf_callchain_entry *trace_in,
>   			    void *buf, u32 size, u64 flags, bool may_fault)
>   {
> -	u32 trace_nr, copy_len, elem_size, num_elem, max_depth;
>   	bool user_build_id = flags & BPF_F_USER_BUILD_ID;
> +	u32 trace_nr, copy_len, elem_size, max_depth;
>   	bool crosstask = task && task != current;
>   	u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
>   	bool user = flags & BPF_F_USER_STACK;
> @@ -438,10 +457,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
>   		goto clear;
>   	}
>   
> -	num_elem = size / elem_size;
> -	max_depth = num_elem + skip;
> -	if (sysctl_perf_event_max_stack < max_depth)
> -		max_depth = sysctl_perf_event_max_stack;
> +	max_depth = stack_map_calculate_max_depth(size, elem_size, flags);
>   
>   	if (may_fault)
>   		rcu_read_lock(); /* need RCU for perf's callchain below */

Re: [PATCH bpf-next v7 3/3] bpf: fix stackmap overflow check in __bpf_get_stackid()

[Song Liu]

On 9/3/25 4:43 PM, Arnaud Lecomte wrote:
> Syzkaller reported a KASAN slab-out-of-bounds write in __bpf_get_stackid()
> when copying stack trace data. The issue occurs when the perf trace
>   contains more stack entries than the stack map bucket can hold,
>   leading to an out-of-bounds write in the bucket's data array.
>
> Changes in v2:
>   - Fixed max_depth names across get stack id
>
> Changes in v4:
>   - Removed unnecessary empty line in __bpf_get_stackid
>
> Changs in v6:
>   - Added back trace_len computation in __bpf_get_stackid
>
> Link to v6: https://lore.kernel.org/all/20250903135348.97884-1-contact@arnaud-lcm.com/
>
> Reported-by: syzbot+c9b724fbb41cf2538b7b@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=c9b724fbb41cf2538b7b
> Fixes: ee2a098851bf ("bpf: Adjust BPF stack helper functions to accommodate skip > 0")
> Signed-off-by: Arnaud Lecomte <contact@arnaud-lcm.com>
> Acked-by: Yonghong Song <yonghong.song@linux.dev>

For future patches, please keep the "Changes in vX.." at the end of

your commit log and after a "---". IOW, something like


Acked-by: Yonghong Song <yonghong.song@linux.dev>

---

changes in v2:

...

---

kernel/bpf/stackmap.c | 8 ++++++++


In this way, the "changes in vXX" part will be removed by git-am.

> ---
>   kernel/bpf/stackmap.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
>
> diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
> index 9f3ae426ddc3..29e05c9ff1bd 100644
> --- a/kernel/bpf/stackmap.c
> +++ b/kernel/bpf/stackmap.c
> @@ -369,6 +369,7 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,
>   {
>   	struct perf_event *event = ctx->event;
>   	struct perf_callchain_entry *trace;
> +	u32 elem_size, max_depth;
>   	bool kernel, user;
>   	__u64 nr_kernel;
>   	int ret;
> @@ -390,11 +391,15 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,
>   		return -EFAULT;
>   
>   	nr_kernel = count_kernel_ip(trace);
> +	elem_size = stack_map_data_size(map);
>   
>   	if (kernel) {
>   		__u64 nr = trace->nr;
>   
>   		trace->nr = nr_kernel;

this trace->nr = is useless.

> +		max_depth =
> +			stack_map_calculate_max_depth(map->value_size, elem_size, flags);
> +		trace->nr = min_t(u32, nr_kernel, max_depth);
>   		ret = __bpf_get_stackid(map, trace, flags);
>   
>   		/* restore nr */
> @@ -407,6 +412,9 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,
>   			return -EFAULT;
>   
>   		flags = (flags & ~BPF_F_SKIP_FIELD_MASK) | skip;
> +		max_depth =
> +			stack_map_calculate_max_depth(map->value_size, elem_size, flags);
> +		trace->nr = min_t(u32, trace->nr, max_depth);
>   		ret = __bpf_get_stackid(map, trace, flags);

I missed this part earlier. Here we need to restore trace->nr, just like 
we did

in the "if (kernel)" branch.

Thanks,

Song

>   	}
>   	return ret;

Re: [PATCH bpf-next v7 2/3] bpf: clean-up bounds checking in __bpf_get_stack

[Lecomte, Arnaud]

On 05/09/2025 00:40, Song Liu wrote:
>
> On 9/3/25 4:40 PM, Arnaud Lecomte wrote:
>> Clean-up bounds checking for trace->nr in
>> __bpf_get_stack by limiting it only to
>> max_depth.
>>
>> Signed-off-by: Arnaud Lecomte <contact@arnaud-lcm.com>
>> Cc: Song Lui <song@kernel.org>
>
> Typo in my name, which is "Song Liu".
>
> This looks right.
>
> Acked-by: Song Liu <song@kernel.org>
>
Oops sorry !
>> ---
>>   kernel/bpf/stackmap.c | 9 +++++----
>>   1 file changed, 5 insertions(+), 4 deletions(-)
>>
>> diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
>> index ed707bc07173..9f3ae426ddc3 100644
>> --- a/kernel/bpf/stackmap.c
>> +++ b/kernel/bpf/stackmap.c
>> @@ -462,13 +462,15 @@ static long __bpf_get_stack(struct pt_regs 
>> *regs, struct task_struct *task,
>>       if (may_fault)
>>           rcu_read_lock(); /* need RCU for perf's callchain below */
>>   -    if (trace_in)
>> +    if (trace_in) {
>>           trace = trace_in;
>> -    else if (kernel && task)
>> +        trace->nr = min_t(u32, trace->nr, max_depth);
>> +    } else if (kernel && task) {
>>           trace = get_callchain_entry_for_task(task, max_depth);
>> -    else
>> +    } else {
>>           trace = get_perf_callchain(regs, 0, kernel, user, max_depth,
>>                          crosstask, false);
>> +    }
>>         if (unlikely(!trace) || trace->nr < skip) {
>>           if (may_fault)
>> @@ -477,7 +479,6 @@ static long __bpf_get_stack(struct pt_regs *regs, 
>> struct task_struct *task,
>>       }
>>         trace_nr = trace->nr - skip;
>> -    trace_nr = (trace_nr <= num_elem) ? trace_nr : num_elem;
>>       copy_len = trace_nr * elem_size;
>>         ips = trace->ip + skip;
>

Re: [PATCH bpf-next v7 3/3] bpf: fix stackmap overflow check in __bpf_get_stackid()

[Lecomte, Arnaud]

On 05/09/2025 00:45, Song Liu wrote:
>
> On 9/3/25 4:43 PM, Arnaud Lecomte wrote:
>> Syzkaller reported a KASAN slab-out-of-bounds write in 
>> __bpf_get_stackid()
>> when copying stack trace data. The issue occurs when the perf trace
>>   contains more stack entries than the stack map bucket can hold,
>>   leading to an out-of-bounds write in the bucket's data array.
>>
>> Changes in v2:
>>   - Fixed max_depth names across get stack id
>>
>> Changes in v4:
>>   - Removed unnecessary empty line in __bpf_get_stackid
>>
>> Changs in v6:
>>   - Added back trace_len computation in __bpf_get_stackid
>>
>> Link to v6: 
>> https://lore.kernel.org/all/20250903135348.97884-1-contact@arnaud-lcm.com/
>>
>> Reported-by: syzbot+c9b724fbb41cf2538b7b@syzkaller.appspotmail.com
>> Closes: https://syzkaller.appspot.com/bug?extid=c9b724fbb41cf2538b7b
>> Fixes: ee2a098851bf ("bpf: Adjust BPF stack helper functions to 
>> accommodate skip > 0")
>> Signed-off-by: Arnaud Lecomte <contact@arnaud-lcm.com>
>> Acked-by: Yonghong Song <yonghong.song@linux.dev>
>
> For future patches, please keep the "Changes in vX.." at the end of
Good to know, thanks !
>
> your commit log and after a "---". IOW, something like
>
>
> Acked-by: Yonghong Song <yonghong.song@linux.dev>
>
> ---
>
> changes in v2:
>
> ...
>
> ---
>
> kernel/bpf/stackmap.c | 8 ++++++++
>
>
> In this way, the "changes in vXX" part will be removed by git-am.
>
>> ---
>>   kernel/bpf/stackmap.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
>> index 9f3ae426ddc3..29e05c9ff1bd 100644
>> --- a/kernel/bpf/stackmap.c
>> +++ b/kernel/bpf/stackmap.c
>> @@ -369,6 +369,7 @@ BPF_CALL_3(bpf_get_stackid_pe, struct 
>> bpf_perf_event_data_kern *, ctx,
>>   {
>>       struct perf_event *event = ctx->event;
>>       struct perf_callchain_entry *trace;
>> +    u32 elem_size, max_depth;
>>       bool kernel, user;
>>       __u64 nr_kernel;
>>       int ret;
>> @@ -390,11 +391,15 @@ BPF_CALL_3(bpf_get_stackid_pe, struct 
>> bpf_perf_event_data_kern *, ctx,
>>           return -EFAULT;
>>         nr_kernel = count_kernel_ip(trace);
>> +    elem_size = stack_map_data_size(map);
>>         if (kernel) {
>>           __u64 nr = trace->nr;
>>             trace->nr = nr_kernel;
>
> this trace->nr = is useless.
>
>> +        max_depth =
>> +            stack_map_calculate_max_depth(map->value_size, 
>> elem_size, flags);
>> +        trace->nr = min_t(u32, nr_kernel, max_depth);
>>           ret = __bpf_get_stackid(map, trace, flags);
>>             /* restore nr */
>> @@ -407,6 +412,9 @@ BPF_CALL_3(bpf_get_stackid_pe, struct 
>> bpf_perf_event_data_kern *, ctx,
>>               return -EFAULT;
>>             flags = (flags & ~BPF_F_SKIP_FIELD_MASK) | skip;
>> +        max_depth =
>> +            stack_map_calculate_max_depth(map->value_size, 
>> elem_size, flags);
>> +        trace->nr = min_t(u32, trace->nr, max_depth);
>>           ret = __bpf_get_stackid(map, trace, flags);
>
> I missed this part earlier. Here we need to restore trace->nr, just 
> like we did

>
> in the "if (kernel)" branch.
>
Make sense, thanks !
> Thanks,
>
> Song
>
>>       }
>>       return ret;
>
Thanks,
Arnaud