In __sanitizer_cov_trace_pc(), previously we write pc before updating pos.
However, some early interrupt code could bypass check_kcov_mode()
check and invoke __sanitizer_cov_trace_pc(). If such interrupt is raised
between writing pc and updating pos, the pc could be overitten by the
recursive __sanitizer_cov_trace_pc().
As suggested by Dmitry, we cold update pos before writing pc to avoid
such interleaving.
Apply the same change to write_comp_data().
Signed-off-by: Congyu Liu <[email protected]>
---
PATCH v2:
* Update pos before writing pc as suggested by Dmitry.
PATCH v1:
https://lore.kernel.org/lkml/[email protected]/
---
kernel/kcov.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/kernel/kcov.c b/kernel/kcov.c
index b3732b210593..e19c84b02452 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -204,8 +204,16 @@ void notrace __sanitizer_cov_trace_pc(void)
/* The first 64-bit word is the number of subsequent PCs. */
pos = READ_ONCE(area[0]) + 1;
if (likely(pos < t->kcov_size)) {
- area[pos] = ip;
+ /* Previously we write pc before updating pos. However, some
+ * early interrupt code could bypass check_kcov_mode() check
+ * and invoke __sanitizer_cov_trace_pc(). If such interrupt is
+ * raised between writing pc and updating pos, the pc could be
+ * overitten by the recursive __sanitizer_cov_trace_pc().
+ * Update pos before writing pc to avoid such interleaving.
+ */
WRITE_ONCE(area[0], pos);
+ barrier();
+ area[pos] = ip;
}
}
EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
@@ -236,11 +244,13 @@ static void notrace write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
start_index = 1 + count * KCOV_WORDS_PER_CMP;
end_pos = (start_index + KCOV_WORDS_PER_CMP) * sizeof(u64);
if (likely(end_pos <= max_pos)) {
+ /* See comment in __sanitizer_cov_trace_pc(). */
+ WRITE_ONCE(area[0], count + 1);
+ barrier();
area[start_index] = type;
area[start_index + 1] = arg1;
area[start_index + 2] = arg2;
area[start_index + 3] = ip;
- WRITE_ONCE(area[0], count + 1);
}
}
--
2.34.1
On Mon, 23 May 2022 at 07:35, Congyu Liu <[email protected]> wrote:
>
> In __sanitizer_cov_trace_pc(), previously we write pc before updating pos.
> However, some early interrupt code could bypass check_kcov_mode()
> check and invoke __sanitizer_cov_trace_pc(). If such interrupt is raised
> between writing pc and updating pos, the pc could be overitten by the
> recursive __sanitizer_cov_trace_pc().
>
> As suggested by Dmitry, we cold update pos before writing pc to avoid
> such interleaving.
>
> Apply the same change to write_comp_data().
>
> Signed-off-by: Congyu Liu <[email protected]>
This version looks good to me.
I wonder how you encountered this? Do you mind sharing a bit about
what you are doing with kcov?
Reviewed-by: Dmitry Vyukov <[email protected]>
Thanks
> ---
> PATCH v2:
> * Update pos before writing pc as suggested by Dmitry.
>
> PATCH v1:
> https://lore.kernel.org/lkml/[email protected]/
> ---
> kernel/kcov.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index b3732b210593..e19c84b02452 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -204,8 +204,16 @@ void notrace __sanitizer_cov_trace_pc(void)
> /* The first 64-bit word is the number of subsequent PCs. */
> pos = READ_ONCE(area[0]) + 1;
> if (likely(pos < t->kcov_size)) {
> - area[pos] = ip;
> + /* Previously we write pc before updating pos. However, some
> + * early interrupt code could bypass check_kcov_mode() check
> + * and invoke __sanitizer_cov_trace_pc(). If such interrupt is
> + * raised between writing pc and updating pos, the pc could be
> + * overitten by the recursive __sanitizer_cov_trace_pc().
> + * Update pos before writing pc to avoid such interleaving.
> + */
> WRITE_ONCE(area[0], pos);
> + barrier();
> + area[pos] = ip;
> }
> }
> EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
> @@ -236,11 +244,13 @@ static void notrace write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
> start_index = 1 + count * KCOV_WORDS_PER_CMP;
> end_pos = (start_index + KCOV_WORDS_PER_CMP) * sizeof(u64);
> if (likely(end_pos <= max_pos)) {
> + /* See comment in __sanitizer_cov_trace_pc(). */
> + WRITE_ONCE(area[0], count + 1);
> + barrier();
> area[start_index] = type;
> area[start_index + 1] = arg1;
> area[start_index + 2] = arg2;
> area[start_index + 3] = ip;
> - WRITE_ONCE(area[0], count + 1);
> }
> }
>
> --
> 2.34.1
>
+Andrew Morton
________________________________________
From: Liu, Congyu <[email protected]>
Sent: Monday, May 23, 2022 23:08
To: Dmitry Vyukov
Cc: [email protected]; [email protected]; [email protected]
Subject: Re: [PATCH v2] kcov: update pos before writing pc in trace function
It was actually first found in the kernel trace module I wrote for my research
project. For each call instruction I instrumented one trace function before it
and one trace function after it, then expected traces generated from
them would match since I only instrumented calls that return. But it turns
out that it didn't match from time to time in a non-deterministic manner.
Eventually I figured out it was actually caused by the overwritten issue
from interrupt. I then referred to kcov for a solution but it also suffered from
the same issue...so here's this patch :).
________________________________________
From: Dmitry Vyukov <[email protected]>
Sent: Monday, May 23, 2022 4:38
To: Liu, Congyu
Cc: [email protected]; [email protected]; [email protected]
Subject: Re: [PATCH v2] kcov: update pos before writing pc in trace function
On Mon, 23 May 2022 at 07:35, Congyu Liu <[email protected]> wrote:
>
> In __sanitizer_cov_trace_pc(), previously we write pc before updating pos.
> However, some early interrupt code could bypass check_kcov_mode()
> check and invoke __sanitizer_cov_trace_pc(). If such interrupt is raised
> between writing pc and updating pos, the pc could be overitten by the
> recursive __sanitizer_cov_trace_pc().
>
> As suggested by Dmitry, we cold update pos before writing pc to avoid
> such interleaving.
>
> Apply the same change to write_comp_data().
>
> Signed-off-by: Congyu Liu <[email protected]>
This version looks good to me.
I wonder how you encountered this? Do you mind sharing a bit about
what you are doing with kcov?
Reviewed-by: Dmitry Vyukov <[email protected]>
Thanks
> ---
> PATCH v2:
> * Update pos before writing pc as suggested by Dmitry.
>
> PATCH v1:
> https://lore.kernel.org/lkml/[email protected]/
> ---
> kernel/kcov.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index b3732b210593..e19c84b02452 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -204,8 +204,16 @@ void notrace __sanitizer_cov_trace_pc(void)
> /* The first 64-bit word is the number of subsequent PCs. */
> pos = READ_ONCE(area[0]) + 1;
> if (likely(pos < t->kcov_size)) {
> - area[pos] = ip;
> + /* Previously we write pc before updating pos. However, some
> + * early interrupt code could bypass check_kcov_mode() check
> + * and invoke __sanitizer_cov_trace_pc(). If such interrupt is
> + * raised between writing pc and updating pos, the pc could be
> + * overitten by the recursive __sanitizer_cov_trace_pc().
> + * Update pos before writing pc to avoid such interleaving.
> + */
> WRITE_ONCE(area[0], pos);
> + barrier();
> + area[pos] = ip;
> }
> }
> EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
> @@ -236,11 +244,13 @@ static void notrace write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
> start_index = 1 + count * KCOV_WORDS_PER_CMP;
> end_pos = (start_index + KCOV_WORDS_PER_CMP) * sizeof(u64);
> if (likely(end_pos <= max_pos)) {
> + /* See comment in __sanitizer_cov_trace_pc(). */
> + WRITE_ONCE(area[0], count + 1);
> + barrier();
> area[start_index] = type;
> area[start_index + 1] = arg1;
> area[start_index + 2] = arg2;
> area[start_index + 3] = ip;
> - WRITE_ONCE(area[0], count + 1);
> }
> }
>
> --
> 2.34.1
>
It was actually first found in the kernel trace module I wrote for my research
project. For each call instruction I instrumented one trace function before it
and one trace function after it, then expected traces generated from
them would match since I only instrumented calls that return. But it turns
out that it didn't match from time to time in a non-deterministic manner.
Eventually I figured out it was actually caused by the overwritten issue
from interrupt. I then referred to kcov for a solution but it also suffered from
the same issue...so here's this patch :).
________________________________________
From: Dmitry Vyukov <[email protected]>
Sent: Monday, May 23, 2022 4:38
To: Liu, Congyu
Cc: [email protected]; [email protected]; [email protected]
Subject: Re: [PATCH v2] kcov: update pos before writing pc in trace function
On Mon, 23 May 2022 at 07:35, Congyu Liu <[email protected]> wrote:
>
> In __sanitizer_cov_trace_pc(), previously we write pc before updating pos.
> However, some early interrupt code could bypass check_kcov_mode()
> check and invoke __sanitizer_cov_trace_pc(). If such interrupt is raised
> between writing pc and updating pos, the pc could be overitten by the
> recursive __sanitizer_cov_trace_pc().
>
> As suggested by Dmitry, we cold update pos before writing pc to avoid
> such interleaving.
>
> Apply the same change to write_comp_data().
>
> Signed-off-by: Congyu Liu <[email protected]>
This version looks good to me.
I wonder how you encountered this? Do you mind sharing a bit about
what you are doing with kcov?
Reviewed-by: Dmitry Vyukov <[email protected]>
Thanks
> ---
> PATCH v2:
> * Update pos before writing pc as suggested by Dmitry.
>
> PATCH v1:
> https://lore.kernel.org/lkml/[email protected]/
> ---
> kernel/kcov.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index b3732b210593..e19c84b02452 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -204,8 +204,16 @@ void notrace __sanitizer_cov_trace_pc(void)
> /* The first 64-bit word is the number of subsequent PCs. */
> pos = READ_ONCE(area[0]) + 1;
> if (likely(pos < t->kcov_size)) {
> - area[pos] = ip;
> + /* Previously we write pc before updating pos. However, some
> + * early interrupt code could bypass check_kcov_mode() check
> + * and invoke __sanitizer_cov_trace_pc(). If such interrupt is
> + * raised between writing pc and updating pos, the pc could be
> + * overitten by the recursive __sanitizer_cov_trace_pc().
> + * Update pos before writing pc to avoid such interleaving.
> + */
> WRITE_ONCE(area[0], pos);
> + barrier();
> + area[pos] = ip;
> }
> }
> EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
> @@ -236,11 +244,13 @@ static void notrace write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
> start_index = 1 + count * KCOV_WORDS_PER_CMP;
> end_pos = (start_index + KCOV_WORDS_PER_CMP) * sizeof(u64);
> if (likely(end_pos <= max_pos)) {
> + /* See comment in __sanitizer_cov_trace_pc(). */
> + WRITE_ONCE(area[0], count + 1);
> + barrier();
> area[start_index] = type;
> area[start_index + 1] = arg1;
> area[start_index + 2] = arg2;
> area[start_index + 3] = ip;
> - WRITE_ONCE(area[0], count + 1);
> }
> }
>
> --
> 2.34.1
>
On Tue, 24 May 2022 at 05:08, Liu, Congyu <[email protected]> wrote:
>
> It was actually first found in the kernel trace module I wrote for my research
> project. For each call instruction I instrumented one trace function before it
> and one trace function after it, then expected traces generated from
> them would match since I only instrumented calls that return. But it turns
> out that it didn't match from time to time in a non-deterministic manner.
> Eventually I figured out it was actually caused by the overwritten issue
> from interrupt. I then referred to kcov for a solution but it also suffered from
> the same issue...so here's this patch :).
Ah, interesting. Thanks for sharing.
> ________________________________________
> From: Dmitry Vyukov <[email protected]>
> Sent: Monday, May 23, 2022 4:38
> To: Liu, Congyu
> Cc: [email protected]; [email protected]; [email protected]
> Subject: Re: [PATCH v2] kcov: update pos before writing pc in trace function
>
> On Mon, 23 May 2022 at 07:35, Congyu Liu <[email protected]> wrote:
> >
> > In __sanitizer_cov_trace_pc(), previously we write pc before updating pos.
> > However, some early interrupt code could bypass check_kcov_mode()
> > check and invoke __sanitizer_cov_trace_pc(). If such interrupt is raised
> > between writing pc and updating pos, the pc could be overitten by the
> > recursive __sanitizer_cov_trace_pc().
> >
> > As suggested by Dmitry, we cold update pos before writing pc to avoid
> > such interleaving.
> >
> > Apply the same change to write_comp_data().
> >
> > Signed-off-by: Congyu Liu <[email protected]>
>
> This version looks good to me.
> I wonder how you encountered this? Do you mind sharing a bit about
> what you are doing with kcov?
>
> Reviewed-by: Dmitry Vyukov <[email protected]>
>
> Thanks
>
> > ---
> > PATCH v2:
> > * Update pos before writing pc as suggested by Dmitry.
> >
> > PATCH v1:
> > https://lore.kernel.org/lkml/[email protected]/
> > ---
> > kernel/kcov.c | 14 ++++++++++++--
> > 1 file changed, 12 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/kcov.c b/kernel/kcov.c
> > index b3732b210593..e19c84b02452 100644
> > --- a/kernel/kcov.c
> > +++ b/kernel/kcov.c
> > @@ -204,8 +204,16 @@ void notrace __sanitizer_cov_trace_pc(void)
> > /* The first 64-bit word is the number of subsequent PCs. */
> > pos = READ_ONCE(area[0]) + 1;
> > if (likely(pos < t->kcov_size)) {
> > - area[pos] = ip;
> > + /* Previously we write pc before updating pos. However, some
> > + * early interrupt code could bypass check_kcov_mode() check
> > + * and invoke __sanitizer_cov_trace_pc(). If such interrupt is
> > + * raised between writing pc and updating pos, the pc could be
> > + * overitten by the recursive __sanitizer_cov_trace_pc().
> > + * Update pos before writing pc to avoid such interleaving.
> > + */
> > WRITE_ONCE(area[0], pos);
> > + barrier();
> > + area[pos] = ip;
> > }
> > }
> > EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
> > @@ -236,11 +244,13 @@ static void notrace write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
> > start_index = 1 + count * KCOV_WORDS_PER_CMP;
> > end_pos = (start_index + KCOV_WORDS_PER_CMP) * sizeof(u64);
> > if (likely(end_pos <= max_pos)) {
> > + /* See comment in __sanitizer_cov_trace_pc(). */
> > + WRITE_ONCE(area[0], count + 1);
> > + barrier();
> > area[start_index] = type;
> > area[start_index + 1] = arg1;
> > area[start_index + 2] = arg2;
> > area[start_index + 3] = ip;
> > - WRITE_ONCE(area[0], count + 1);
> > }
> > }
> >
> > --
> > 2.34.1
> >