2020-03-06 08:11:48

by Artem Savkov

Subject: [PATCH] ftrace: return first found result in lookup_rec()

It appears that ip ranges can overlap so. In that case lookup_rec()
returns whatever results it got last even if it found nothing in last
searched page.

This breaks an obscure livepatch late module patching usecase:
- load livepatch
- load the patched module
- unload livepatch
- try to load livepatch again

To fix this return from lookup_rec() as soon as it found the record
containing searched-for ip. This used to be this way prior lookup_rec()
introduction.

Fixes: 7e16f581a817 ("ftrace: Separate out functionality from ftrace_location_range()")
Signed-off-by: Artem Savkov <[email protected]>
---
kernel/trace/ftrace.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 3f7ee102868a..b0f5ee1fd6e4 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1547,8 +1547,10 @@ static struct dyn_ftrace *lookup_rec(unsigned long start, unsigned long end)
rec = bsearch(&key, pg->records, pg->index,
sizeof(struct dyn_ftrace),
ftrace_cmp_recs);
+ if (rec)
+ return rec;
}
- return rec;
+ return NULL;
}

/**
--
2.21.1

2020-03-06 17:13:21

by Steven Rostedt

Subject: Re: [PATCH] ftrace: return first found result in lookup_rec()

On Fri, 6 Mar 2020 09:10:35 +0100
Artem Savkov <[email protected]> wrote:

> It appears that ip ranges can overlap so. In that case lookup_rec()
> returns whatever results it got last even if it found nothing in last
> searched page.
>
> This breaks an obscure livepatch late module patching usecase:
> - load livepatch
> - load the patched module
> - unload livepatch
> - try to load livepatch again
>
> To fix this return from lookup_rec() as soon as it found the record
> containing searched-for ip. This used to be this way prior lookup_rec()
> introduction.
>
> Fixes: 7e16f581a817 ("ftrace: Separate out functionality from ftrace_location_range()")
> Signed-off-by: Artem Savkov <[email protected]>
> ---
> kernel/trace/ftrace.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 3f7ee102868a..b0f5ee1fd6e4 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -1547,8 +1547,10 @@ static struct dyn_ftrace *lookup_rec(unsigned long start, unsigned long end)
> rec = bsearch(&key, pg->records, pg->index,
> sizeof(struct dyn_ftrace),
> ftrace_cmp_recs);

how about just adding:

if (rec)
break;

as that will do the same thing without adding two returns.

-- Steve

> + if (rec)
> + return rec;
> }
> - return rec;
> + return NULL;
> }
>
> /**

2020-03-06 17:43:57

by Artem Savkov

Subject: [PATCH v2] ftrace: return first found result in lookup_rec()

It appears that ip ranges can overlap so. In that case lookup_rec()
returns whatever results it got last even if it found nothing in last
searched page.

This breaks an obscure livepatch late module patching usecase:
- load livepatch
- load the patched module
- unload livepatch
- try to load livepatch again

To fix this return from lookup_rec() as soon as it found the record
containing searched-for ip. This used to be this way prior lookup_rec()
introduction.

v2: break instead of two returns

Fixes: 7e16f581a817 ("ftrace: Separate out functionality from ftrace_location_range()")
Signed-off-by: Artem Savkov <[email protected]>
---
kernel/trace/ftrace.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 3f7ee102868a..fd81c7de77a7 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1547,6 +1547,8 @@ static struct dyn_ftrace *lookup_rec(unsigned long start, unsigned long end)
rec = bsearch(&key, pg->records, pg->index,
sizeof(struct dyn_ftrace),
ftrace_cmp_recs);
+ if (rec)
+ break;
}
return rec;
}
--
2.21.1

2020-03-10 19:39:56

by Steven Rostedt

Subject: Re: [PATCH v2] ftrace: return first found result in lookup_rec()

On Fri, 6 Mar 2020 18:43:17 +0100
Artem Savkov <[email protected]> wrote:

> It appears that ip ranges can overlap so. In that case lookup_rec()
> returns whatever results it got last even if it found nothing in last
> searched page.
>
> This breaks an obscure livepatch late module patching usecase:
> - load livepatch
> - load the patched module
> - unload livepatch
> - try to load livepatch again
>
> To fix this return from lookup_rec() as soon as it found the record
> containing searched-for ip. This used to be this way prior lookup_rec()
> introduction.
>
> v2: break instead of two returns

Thanks Artem, I applied your patch. But just an FYI, it's best to place the
"v2" statement below the three dashes "---" so that it doesn't get pulled
into the git commit when this patch is applied via a script.

-- Steve

>
> Fixes: 7e16f581a817 ("ftrace: Separate out functionality from ftrace_location_range()")
> Signed-off-by: Artem Savkov <[email protected]>
> ---
> kernel/trace/ftrace.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 3f7ee102868a..fd81c7de77a7 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -1547,6 +1547,8 @@ static struct dyn_ftrace *lookup_rec(unsigned long start, unsigned long end)
> rec = bsearch(&key, pg->records, pg->index,
> sizeof(struct dyn_ftrace),
> ftrace_cmp_recs);
> + if (rec)
> + break;
> }
> return rec;
> }