* [PATCH bpf-next] bpf, seccomp: fix false positive preemption splat for cbpf->ebpf progs
@ 2019-02-20 11:06 Daniel Borkmann
2019-02-20 17:07 ` Alexei Starovoitov
0 siblings, 1 reply; 4+ messages in thread
From: Daniel Borkmann @ 2019-02-20 11:06 UTC (permalink / raw)
To: ast; +Cc: netdev, Daniel Borkmann
In 568f196756ad ("bpf: check that BPF programs run with preemption disabled")
a check was added for BPF_PROG_RUN() that for every invocation preemption has
to be disabled to not break eBPF assumptions (e.g. per-cpu map). Of course this
does not count for seccomp because only cBPF -> eBPF is loaded here and it does
not make use of any functionality that would require this assertion. Fix this
false positive by adding and using __BPF_PROG_RUN() variant that does not have
the cant_sleep(); check.
Fixes: 568f196756ad ("bpf: check that BPF programs run with preemption disabled")
Reported-by: syzbot+8bf19ee2aa580de7a2a7@syzkaller.appspotmail.com
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---
include/linux/filter.h | 9 ++++++++-
kernel/seccomp.c | 2 +-
2 files changed, 9 insertions(+), 2 deletions(-)
diff --git a/include/linux/filter.h b/include/linux/filter.h
index f32b3ec..2648fd7 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -533,7 +533,14 @@ struct sk_filter {
struct bpf_prog *prog;
};
-#define BPF_PROG_RUN(filter, ctx) ({ cant_sleep(); (*(filter)->bpf_func)(ctx, (filter)->insnsi); })
+#define bpf_prog_run__non_preempt(prog, ctx) \
+ ({ cant_sleep(); __BPF_PROG_RUN(prog, ctx); })
+/* Native eBPF or cBPF -> eBPF transitions. Preemption must be disabled. */
+#define BPF_PROG_RUN(prog, ctx) \
+ bpf_prog_run__non_preempt(prog, ctx)
+/* Direct use for cBPF -> eBPF only, but not for native eBPF. */
+#define __BPF_PROG_RUN(prog, ctx) \
+ (*(prog)->bpf_func)(ctx, (prog)->insnsi)
#define BPF_SKB_CB_LEN QDISC_CB_PRIV_LEN
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index e815781..826d4e4 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -268,7 +268,7 @@ static u32 seccomp_run_filters(const struct seccomp_data *sd,
* value always takes priority (ignoring the DATA).
*/
for (; f; f = f->prev) {
- u32 cur_ret = BPF_PROG_RUN(f->prog, sd);
+ u32 cur_ret = __BPF_PROG_RUN(f->prog, sd);
if (ACTION_ONLY(cur_ret) < ACTION_ONLY(ret)) {
ret = cur_ret;
--
2.9.5
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH bpf-next] bpf, seccomp: fix false positive preemption splat for cbpf->ebpf progs
2019-02-20 11:06 [PATCH bpf-next] bpf, seccomp: fix false positive preemption splat for cbpf->ebpf progs Daniel Borkmann
@ 2019-02-20 17:07 ` Alexei Starovoitov
2019-02-20 18:27 ` Daniel Borkmann
0 siblings, 1 reply; 4+ messages in thread
From: Alexei Starovoitov @ 2019-02-20 17:07 UTC (permalink / raw)
To: Daniel Borkmann; +Cc: ast, netdev
On Wed, Feb 20, 2019 at 12:06:29PM +0100, Daniel Borkmann wrote:
> In 568f196756ad ("bpf: check that BPF programs run with preemption disabled")
> a check was added for BPF_PROG_RUN() that for every invocation preemption has
> to be disabled to not break eBPF assumptions (e.g. per-cpu map). Of course this
> does not count for seccomp because only cBPF -> eBPF is loaded here and it does
> not make use of any functionality that would require this assertion. Fix this
> false positive by adding and using __BPF_PROG_RUN() variant that does not have
> the cant_sleep(); check.
>
> Fixes: 568f196756ad ("bpf: check that BPF programs run with preemption disabled")
> Reported-by: syzbot+8bf19ee2aa580de7a2a7@syzkaller.appspotmail.com
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> ---
> include/linux/filter.h | 9 ++++++++-
> kernel/seccomp.c | 2 +-
> 2 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index f32b3ec..2648fd7 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -533,7 +533,14 @@ struct sk_filter {
> struct bpf_prog *prog;
> };
>
> -#define BPF_PROG_RUN(filter, ctx) ({ cant_sleep(); (*(filter)->bpf_func)(ctx, (filter)->insnsi); })
> +#define bpf_prog_run__non_preempt(prog, ctx) \
> + ({ cant_sleep(); __BPF_PROG_RUN(prog, ctx); })
> +/* Native eBPF or cBPF -> eBPF transitions. Preemption must be disabled. */
> +#define BPF_PROG_RUN(prog, ctx) \
> + bpf_prog_run__non_preempt(prog, ctx)
> +/* Direct use for cBPF -> eBPF only, but not for native eBPF. */
I think the comment is too abstract.
May be it should say that this is seccomp cBPF only ?
And macro name should be explicit as well ?
> +#define __BPF_PROG_RUN(prog, ctx) \
> + (*(prog)->bpf_func)(ctx, (prog)->insnsi)
>
> #define BPF_SKB_CB_LEN QDISC_CB_PRIV_LEN
>
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index e815781..826d4e4 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -268,7 +268,7 @@ static u32 seccomp_run_filters(const struct seccomp_data *sd,
> * value always takes priority (ignoring the DATA).
> */
> for (; f; f = f->prev) {
> - u32 cur_ret = BPF_PROG_RUN(f->prog, sd);
> + u32 cur_ret = __BPF_PROG_RUN(f->prog, sd);
>
> if (ACTION_ONLY(cur_ret) < ACTION_ONLY(ret)) {
> ret = cur_ret;
> --
> 2.9.5
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH bpf-next] bpf, seccomp: fix false positive preemption splat for cbpf->ebpf progs
2019-02-20 17:07 ` Alexei Starovoitov
@ 2019-02-20 18:27 ` Daniel Borkmann
2019-02-20 18:34 ` Alexei Starovoitov
0 siblings, 1 reply; 4+ messages in thread
From: Daniel Borkmann @ 2019-02-20 18:27 UTC (permalink / raw)
To: Alexei Starovoitov; +Cc: ast, netdev
On 02/20/2019 06:07 PM, Alexei Starovoitov wrote:
> On Wed, Feb 20, 2019 at 12:06:29PM +0100, Daniel Borkmann wrote:
>> In 568f196756ad ("bpf: check that BPF programs run with preemption disabled")
>> a check was added for BPF_PROG_RUN() that for every invocation preemption has
>> to be disabled to not break eBPF assumptions (e.g. per-cpu map). Of course this
>> does not count for seccomp because only cBPF -> eBPF is loaded here and it does
>> not make use of any functionality that would require this assertion. Fix this
>> false positive by adding and using __BPF_PROG_RUN() variant that does not have
>> the cant_sleep(); check.
>>
>> Fixes: 568f196756ad ("bpf: check that BPF programs run with preemption disabled")
>> Reported-by: syzbot+8bf19ee2aa580de7a2a7@syzkaller.appspotmail.com
>> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
>> ---
>> include/linux/filter.h | 9 ++++++++-
>> kernel/seccomp.c | 2 +-
>> 2 files changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/filter.h b/include/linux/filter.h
>> index f32b3ec..2648fd7 100644
>> --- a/include/linux/filter.h
>> +++ b/include/linux/filter.h
>> @@ -533,7 +533,14 @@ struct sk_filter {
>> struct bpf_prog *prog;
>> };
>>
>> -#define BPF_PROG_RUN(filter, ctx) ({ cant_sleep(); (*(filter)->bpf_func)(ctx, (filter)->insnsi); })
>> +#define bpf_prog_run__non_preempt(prog, ctx) \
>> + ({ cant_sleep(); __BPF_PROG_RUN(prog, ctx); })
>> +/* Native eBPF or cBPF -> eBPF transitions. Preemption must be disabled. */
>> +#define BPF_PROG_RUN(prog, ctx) \
>> + bpf_prog_run__non_preempt(prog, ctx)
>> +/* Direct use for cBPF -> eBPF only, but not for native eBPF. */
>
> I think the comment is too abstract.
> May be it should say that this is seccomp cBPF only ?
> And macro name should be explicit as well ?
I think macro naming is probably okay imho as used internally as
well from BPF_PROG_RUN(), but I'll improve the comment to state
seccomp specifically as an example there and providing some more
background.
>> +#define __BPF_PROG_RUN(prog, ctx) \
>> + (*(prog)->bpf_func)(ctx, (prog)->insnsi)
>>
>> #define BPF_SKB_CB_LEN QDISC_CB_PRIV_LEN
>>
>> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
>> index e815781..826d4e4 100644
>> --- a/kernel/seccomp.c
>> +++ b/kernel/seccomp.c
>> @@ -268,7 +268,7 @@ static u32 seccomp_run_filters(const struct seccomp_data *sd,
>> * value always takes priority (ignoring the DATA).
>> */
>> for (; f; f = f->prev) {
>> - u32 cur_ret = BPF_PROG_RUN(f->prog, sd);
>> + u32 cur_ret = __BPF_PROG_RUN(f->prog, sd);
>>
>> if (ACTION_ONLY(cur_ret) < ACTION_ONLY(ret)) {
>> ret = cur_ret;
>> --
>> 2.9.5
>>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH bpf-next] bpf, seccomp: fix false positive preemption splat for cbpf->ebpf progs
2019-02-20 18:27 ` Daniel Borkmann
@ 2019-02-20 18:34 ` Alexei Starovoitov
0 siblings, 0 replies; 4+ messages in thread
From: Alexei Starovoitov @ 2019-02-20 18:34 UTC (permalink / raw)
To: Daniel Borkmann; +Cc: Alexei Starovoitov, Network Development
On Wed, Feb 20, 2019 at 10:27 AM Daniel Borkmann <daniel@iogearbox.net> wrote:
>
> On 02/20/2019 06:07 PM, Alexei Starovoitov wrote:
> > On Wed, Feb 20, 2019 at 12:06:29PM +0100, Daniel Borkmann wrote:
> >> In 568f196756ad ("bpf: check that BPF programs run with preemption disabled")
> >> a check was added for BPF_PROG_RUN() that for every invocation preemption has
> >> to be disabled to not break eBPF assumptions (e.g. per-cpu map). Of course this
> >> does not count for seccomp because only cBPF -> eBPF is loaded here and it does
> >> not make use of any functionality that would require this assertion. Fix this
> >> false positive by adding and using __BPF_PROG_RUN() variant that does not have
> >> the cant_sleep(); check.
> >>
> >> Fixes: 568f196756ad ("bpf: check that BPF programs run with preemption disabled")
> >> Reported-by: syzbot+8bf19ee2aa580de7a2a7@syzkaller.appspotmail.com
> >> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> >> ---
> >> include/linux/filter.h | 9 ++++++++-
> >> kernel/seccomp.c | 2 +-
> >> 2 files changed, 9 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/include/linux/filter.h b/include/linux/filter.h
> >> index f32b3ec..2648fd7 100644
> >> --- a/include/linux/filter.h
> >> +++ b/include/linux/filter.h
> >> @@ -533,7 +533,14 @@ struct sk_filter {
> >> struct bpf_prog *prog;
> >> };
> >>
> >> -#define BPF_PROG_RUN(filter, ctx) ({ cant_sleep(); (*(filter)->bpf_func)(ctx, (filter)->insnsi); })
> >> +#define bpf_prog_run__non_preempt(prog, ctx) \
> >> + ({ cant_sleep(); __BPF_PROG_RUN(prog, ctx); })
> >> +/* Native eBPF or cBPF -> eBPF transitions. Preemption must be disabled. */
> >> +#define BPF_PROG_RUN(prog, ctx) \
> >> + bpf_prog_run__non_preempt(prog, ctx)
> >> +/* Direct use for cBPF -> eBPF only, but not for native eBPF. */
> >
> > I think the comment is too abstract.
> > May be it should say that this is seccomp cBPF only ?
> > And macro name should be explicit as well ?
>
> I think macro naming is probably okay imho as used internally as
> well from BPF_PROG_RUN(), but I'll improve the comment to state
> seccomp specifically as an example there and providing some more
> background.
I'm worried about misuse of the macro.
If there was a word seccomp in it it would made people
think much harder before calling it.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2019-02-20 18:35 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2019-02-20 11:06 [PATCH bpf-next] bpf, seccomp: fix false positive preemption splat for cbpf->ebpf progs Daniel Borkmann
2019-02-20 17:07 ` Alexei Starovoitov
2019-02-20 18:27 ` Daniel Borkmann
2019-02-20 18:34 ` Alexei Starovoitov
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