[PATCH] uprobes: Fix race in uprobe_free_utask

[PATCH] uprobes: Fix race in uprobe_free_utask

[Jiri Olsa]

Max Makarov reported kernel panic [1] in perf user callchain code.

The reason for that is the race between uprobe_free_utask and bpf
profiler code doing the perf user stack unwind and is triggered
within uprobe_free_utask function:
  - after current->utask is freed and
  - before current->utask is set to NULL

 general protection fault, probably for non-canonical address 0x9e759c37ee555c76: 0000 [#1] SMP PTI
 RIP: 0010:is_uprobe_at_func_entry+0x28/0x80
 ...
  ? die_addr+0x36/0x90
  ? exc_general_protection+0x217/0x420
  ? asm_exc_general_protection+0x26/0x30
  ? is_uprobe_at_func_entry+0x28/0x80
  perf_callchain_user+0x20a/0x360
  get_perf_callchain+0x147/0x1d0
  bpf_get_stackid+0x60/0x90
  bpf_prog_9aac297fb833e2f5_do_perf_event+0x434/0x53b
  ? __smp_call_single_queue+0xad/0x120
  bpf_overflow_handler+0x75/0x110
  ...
  asm_sysvec_apic_timer_interrupt+0x1a/0x20
 RIP: 0010:__kmem_cache_free+0x1cb/0x350
 ...
  ? uprobe_free_utask+0x62/0x80
  ? acct_collect+0x4c/0x220
  uprobe_free_utask+0x62/0x80
  mm_release+0x12/0xb0
  do_exit+0x26b/0xaa0
  __x64_sys_exit+0x1b/0x20
  do_syscall_64+0x5a/0x80

It can be easily reproduced by running following commands in
separate terminals:

  # while :; do bpftrace -e 'uprobe:/bin/ls:_start  { printf("hit\n"); }' -c ls; done
  # bpftrace -e 'profile:hz:100000 { @[ustack()] = count(); }'

Fixing this by making sure current->utask pointer is set to NULL
before we start to release the utask object.

[1] https://github.com/grafana/pyroscope/issues/3673
Reported-by: Max Makarov <maxpain@linux.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 kernel/events/uprobes.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index fa04b14a7d72..5d71ef85420c 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1915,6 +1915,7 @@ void uprobe_free_utask(struct task_struct *t)
 	if (!utask)
 		return;
 
+	t->utask = NULL;
 	WARN_ON_ONCE(utask->active_uprobe || utask->xol_vaddr);
 
 	timer_delete_sync(&utask->ri_timer);
@@ -1924,7 +1925,6 @@ void uprobe_free_utask(struct task_struct *t)
 		ri = free_ret_instance(ri, true /* cleanup_hprobe */);
 
 	kfree(utask);
-	t->utask = NULL;
 }
 
 #define RI_TIMER_PERIOD (HZ / 10) /* 100 ms */
-- 
2.47.0

Re: [PATCH] uprobes: Fix race in uprobe_free_utask

[Oleg Nesterov]

On 01/09, Jiri Olsa wrote:
>
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1915,6 +1915,7 @@ void uprobe_free_utask(struct task_struct *t)
>  	if (!utask)
>  		return;
>
> +	t->utask = NULL;
>  	WARN_ON_ONCE(utask->active_uprobe || utask->xol_vaddr);
>
>  	timer_delete_sync(&utask->ri_timer);
> @@ -1924,7 +1925,6 @@ void uprobe_free_utask(struct task_struct *t)
>  		ri = free_ret_instance(ri, true /* cleanup_hprobe */);
>
>  	kfree(utask);
> -	t->utask = NULL;

Acked-by: Oleg Nesterov <oleg@redhat.com>

Re: [PATCH] uprobes: Fix race in uprobe_free_utask

[Daniel Borkmann]

On 1/9/25 3:14 PM, Jiri Olsa wrote:
> Max Makarov reported kernel panic [1] in perf user callchain code.
> 
> The reason for that is the race between uprobe_free_utask and bpf
> profiler code doing the perf user stack unwind and is triggered
> within uprobe_free_utask function:
>    - after current->utask is freed and
>    - before current->utask is set to NULL
> 
>   general protection fault, probably for non-canonical address 0x9e759c37ee555c76: 0000 [#1] SMP PTI
>   RIP: 0010:is_uprobe_at_func_entry+0x28/0x80
>   ...
>    ? die_addr+0x36/0x90
>    ? exc_general_protection+0x217/0x420
>    ? asm_exc_general_protection+0x26/0x30
>    ? is_uprobe_at_func_entry+0x28/0x80
>    perf_callchain_user+0x20a/0x360
>    get_perf_callchain+0x147/0x1d0
>    bpf_get_stackid+0x60/0x90
>    bpf_prog_9aac297fb833e2f5_do_perf_event+0x434/0x53b
>    ? __smp_call_single_queue+0xad/0x120
>    bpf_overflow_handler+0x75/0x110
>    ...
>    asm_sysvec_apic_timer_interrupt+0x1a/0x20
>   RIP: 0010:__kmem_cache_free+0x1cb/0x350
>   ...
>    ? uprobe_free_utask+0x62/0x80
>    ? acct_collect+0x4c/0x220
>    uprobe_free_utask+0x62/0x80
>    mm_release+0x12/0xb0
>    do_exit+0x26b/0xaa0
>    __x64_sys_exit+0x1b/0x20
>    do_syscall_64+0x5a/0x80
> 
> It can be easily reproduced by running following commands in
> separate terminals:
> 
>    # while :; do bpftrace -e 'uprobe:/bin/ls:_start  { printf("hit\n"); }' -c ls; done
>    # bpftrace -e 'profile:hz:100000 { @[ustack()] = count(); }'
> 
> Fixing this by making sure current->utask pointer is set to NULL
> before we start to release the utask object.

Lets add Fixes tag for stable team:

Fixes: cfa7f3d2c526 ("perf,x86: avoid missing caller address in stack traces captured in uprobe")

> [1] https://github.com/grafana/pyroscope/issues/3673
> Reported-by: Max Makarov <maxpain@linux.com>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>

fwiw, the other version we were potentially thinking of was below, but
just moving the t->utask NULL assignment seemed better.

Thanks,
Daniel

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index c75c482d4c52..05f9cedf2691 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2835,6 +2835,8 @@ static bool is_uprobe_at_func_entry(struct pt_regs *regs)

         if (!current->utask)
                 return false;
+       if (!current->utask->active_uprobe)
+               return false;

         auprobe = current->utask->auprobe;
         if (!auprobe)

Re: [PATCH] uprobes: Fix race in uprobe_free_utask

[Jiri Olsa]

On Thu, Jan 09, 2025 at 03:41:26PM +0100, Daniel Borkmann wrote:
> On 1/9/25 3:14 PM, Jiri Olsa wrote:
> > Max Makarov reported kernel panic [1] in perf user callchain code.
> > 
> > The reason for that is the race between uprobe_free_utask and bpf
> > profiler code doing the perf user stack unwind and is triggered
> > within uprobe_free_utask function:
> >    - after current->utask is freed and
> >    - before current->utask is set to NULL
> > 
> >   general protection fault, probably for non-canonical address 0x9e759c37ee555c76: 0000 [#1] SMP PTI
> >   RIP: 0010:is_uprobe_at_func_entry+0x28/0x80
> >   ...
> >    ? die_addr+0x36/0x90
> >    ? exc_general_protection+0x217/0x420
> >    ? asm_exc_general_protection+0x26/0x30
> >    ? is_uprobe_at_func_entry+0x28/0x80
> >    perf_callchain_user+0x20a/0x360
> >    get_perf_callchain+0x147/0x1d0
> >    bpf_get_stackid+0x60/0x90
> >    bpf_prog_9aac297fb833e2f5_do_perf_event+0x434/0x53b
> >    ? __smp_call_single_queue+0xad/0x120
> >    bpf_overflow_handler+0x75/0x110
> >    ...
> >    asm_sysvec_apic_timer_interrupt+0x1a/0x20
> >   RIP: 0010:__kmem_cache_free+0x1cb/0x350
> >   ...
> >    ? uprobe_free_utask+0x62/0x80
> >    ? acct_collect+0x4c/0x220
> >    uprobe_free_utask+0x62/0x80
> >    mm_release+0x12/0xb0
> >    do_exit+0x26b/0xaa0
> >    __x64_sys_exit+0x1b/0x20
> >    do_syscall_64+0x5a/0x80
> > 
> > It can be easily reproduced by running following commands in
> > separate terminals:
> > 
> >    # while :; do bpftrace -e 'uprobe:/bin/ls:_start  { printf("hit\n"); }' -c ls; done
> >    # bpftrace -e 'profile:hz:100000 { @[ustack()] = count(); }'
> > 
> > Fixing this by making sure current->utask pointer is set to NULL
> > before we start to release the utask object.
> 
> Lets add Fixes tag for stable team:
> 
> Fixes: cfa7f3d2c526 ("perf,x86: avoid missing caller address in stack traces captured in uprobe")

ugh right, thanks for finding that

jirka

> 
> > [1] https://github.com/grafana/pyroscope/issues/3673
> > Reported-by: Max Makarov <maxpain@linux.com>
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> 
> fwiw, the other version we were potentially thinking of was below, but
> just moving the t->utask NULL assignment seemed better.
> 
> Thanks,
> Daniel
> 
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index c75c482d4c52..05f9cedf2691 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -2835,6 +2835,8 @@ static bool is_uprobe_at_func_entry(struct pt_regs *regs)
> 
>         if (!current->utask)
>                 return false;
> +       if (!current->utask->active_uprobe)
> +               return false;
> 
>         auprobe = current->utask->auprobe;
>         if (!auprobe)

Re: [PATCH] uprobes: Fix race in uprobe_free_utask

[Andrii Nakryiko]

On Thu, Jan 9, 2025 at 6:14 AM Jiri Olsa <jolsa@kernel.org> wrote:
>
> Max Makarov reported kernel panic [1] in perf user callchain code.
>
> The reason for that is the race between uprobe_free_utask and bpf
> profiler code doing the perf user stack unwind and is triggered
> within uprobe_free_utask function:
>   - after current->utask is freed and
>   - before current->utask is set to NULL
>
>  general protection fault, probably for non-canonical address 0x9e759c37ee555c76: 0000 [#1] SMP PTI
>  RIP: 0010:is_uprobe_at_func_entry+0x28/0x80
>  ...
>   ? die_addr+0x36/0x90
>   ? exc_general_protection+0x217/0x420
>   ? asm_exc_general_protection+0x26/0x30
>   ? is_uprobe_at_func_entry+0x28/0x80
>   perf_callchain_user+0x20a/0x360
>   get_perf_callchain+0x147/0x1d0
>   bpf_get_stackid+0x60/0x90
>   bpf_prog_9aac297fb833e2f5_do_perf_event+0x434/0x53b
>   ? __smp_call_single_queue+0xad/0x120
>   bpf_overflow_handler+0x75/0x110
>   ...
>   asm_sysvec_apic_timer_interrupt+0x1a/0x20
>  RIP: 0010:__kmem_cache_free+0x1cb/0x350
>  ...
>   ? uprobe_free_utask+0x62/0x80
>   ? acct_collect+0x4c/0x220
>   uprobe_free_utask+0x62/0x80
>   mm_release+0x12/0xb0
>   do_exit+0x26b/0xaa0
>   __x64_sys_exit+0x1b/0x20
>   do_syscall_64+0x5a/0x80
>
> It can be easily reproduced by running following commands in
> separate terminals:
>
>   # while :; do bpftrace -e 'uprobe:/bin/ls:_start  { printf("hit\n"); }' -c ls; done
>   # bpftrace -e 'profile:hz:100000 { @[ustack()] = count(); }'
>
> Fixing this by making sure current->utask pointer is set to NULL
> before we start to release the utask object.
>
> [1] https://github.com/grafana/pyroscope/issues/3673
> Reported-by: Max Makarov <maxpain@linux.com>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
>  kernel/events/uprobes.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>

ah, it's interrupt/NMI checking current->utask, makes total sense,
thanks for the fix!

Acked-by: Andrii Nakryiko <andrii@kernel.org>

> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index fa04b14a7d72..5d71ef85420c 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1915,6 +1915,7 @@ void uprobe_free_utask(struct task_struct *t)
>         if (!utask)
>                 return;
>
> +       t->utask = NULL;
>         WARN_ON_ONCE(utask->active_uprobe || utask->xol_vaddr);
>
>         timer_delete_sync(&utask->ri_timer);
> @@ -1924,7 +1925,6 @@ void uprobe_free_utask(struct task_struct *t)
>                 ri = free_ret_instance(ri, true /* cleanup_hprobe */);
>
>         kfree(utask);
> -       t->utask = NULL;
>  }
>
>  #define RI_TIMER_PERIOD (HZ / 10) /* 100 ms */
> --
> 2.47.0
>