2023-04-03 22:04:43

by Jiri Olsa

Subject: [PATCH bpf-next] kallsyms: Disable preemption for find_kallsyms_symbol_value

Artem reported suspicious RCU usage [1]. The reason is that verifier
calls find_kallsyms_symbol_value with preemption enabled which will
trigger suspicious RCU usage warning in rcu_dereference_sched call.

Disabling preemption in find_kallsyms_symbol_value and adding
__find_kallsyms_symbol_value function.

Fixes: 31bf1dbccfb0 ("bpf: Fix attaching fentry/fexit/fmod_ret/lsm to modules")
[1] https://lore.kernel.org/bpf/[email protected]/
Reported-by: Artem Savkov <[email protected]>
Signed-off-by: Jiri Olsa <[email protected]>
---
kernel/module/kallsyms.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
index ab2376a1be88..bdc911dbcde5 100644
--- a/kernel/module/kallsyms.c
+++ b/kernel/module/kallsyms.c
@@ -442,7 +442,7 @@ int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
}

/* Given a module and name of symbol, find and return the symbol's value */
-unsigned long find_kallsyms_symbol_value(struct module *mod, const char *name)
+static unsigned long __find_kallsyms_symbol_value(struct module *mod, const char *name)
{
unsigned int i;
struct mod_kallsyms *kallsyms = rcu_dereference_sched(mod->kallsyms);
@@ -466,7 +466,7 @@ static unsigned long __module_kallsyms_lookup_name(const char *name)
if (colon) {
mod = find_module_all(name, colon - name, false);
if (mod)
- return find_kallsyms_symbol_value(mod, colon + 1);
+ return __find_kallsyms_symbol_value(mod, colon + 1);
return 0;
}

@@ -475,7 +475,7 @@ static unsigned long __module_kallsyms_lookup_name(const char *name)

if (mod->state == MODULE_STATE_UNFORMED)
continue;
- ret = find_kallsyms_symbol_value(mod, name);
+ ret = __find_kallsyms_symbol_value(mod, name);
if (ret)
return ret;
}
@@ -494,6 +494,16 @@ unsigned long module_kallsyms_lookup_name(const char *name)
return ret;
}

+unsigned long find_kallsyms_symbol_value(struct module *mod, const char *name)
+{
+ unsigned long ret;
+
+ preempt_disable();
+ ret = __find_kallsyms_symbol_value(mod, name);
+ preempt_enable();
+ return ret;
+}
+
int module_kallsyms_on_each_symbol(const char *modname,
int (*fn)(void *, const char *,
struct module *, unsigned long),
--
2.39.2

2023-04-04 07:00:53

by Artem Savkov

Subject: Re: [PATCH bpf-next] kallsyms: Disable preemption for find_kallsyms_symbol_value

On Tue, Apr 04, 2023 at 12:02:54AM +0200, Jiri Olsa wrote:
> Artem reported suspicious RCU usage [1]. The reason is that verifier
> calls find_kallsyms_symbol_value with preemption enabled which will
> trigger suspicious RCU usage warning in rcu_dereference_sched call.
>
> Disabling preemption in find_kallsyms_symbol_value and adding
> __find_kallsyms_symbol_value function.

Tested-by: Artem Savkov <[email protected]>

> Fixes: 31bf1dbccfb0 ("bpf: Fix attaching fentry/fexit/fmod_ret/lsm to modules")
> [1] https://lore.kernel.org/bpf/[email protected]/
> Reported-by: Artem Savkov <[email protected]>
> Signed-off-by: Jiri Olsa <[email protected]>
> ---
> kernel/module/kallsyms.c | 16 +++++++++++++---
> 1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
> index ab2376a1be88..bdc911dbcde5 100644
> --- a/kernel/module/kallsyms.c
> +++ b/kernel/module/kallsyms.c
> @@ -442,7 +442,7 @@ int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
> }
>
> /* Given a module and name of symbol, find and return the symbol's value */
> -unsigned long find_kallsyms_symbol_value(struct module *mod, const char *name)
> +static unsigned long __find_kallsyms_symbol_value(struct module *mod, const char *name)
> {
> unsigned int i;
> struct mod_kallsyms *kallsyms = rcu_dereference_sched(mod->kallsyms);
> @@ -466,7 +466,7 @@ static unsigned long __module_kallsyms_lookup_name(const char *name)
> if (colon) {
> mod = find_module_all(name, colon - name, false);
> if (mod)
> - return find_kallsyms_symbol_value(mod, colon + 1);
> + return __find_kallsyms_symbol_value(mod, colon + 1);
> return 0;
> }
>
> @@ -475,7 +475,7 @@ static unsigned long __module_kallsyms_lookup_name(const char *name)
>
> if (mod->state == MODULE_STATE_UNFORMED)
> continue;
> - ret = find_kallsyms_symbol_value(mod, name);
> + ret = __find_kallsyms_symbol_value(mod, name);
> if (ret)
> return ret;
> }
> @@ -494,6 +494,16 @@ unsigned long module_kallsyms_lookup_name(const char *name)
> return ret;
> }
>
> +unsigned long find_kallsyms_symbol_value(struct module *mod, const char *name)
> +{
> + unsigned long ret;
> +
> + preempt_disable();
> + ret = __find_kallsyms_symbol_value(mod, name);
> + preempt_enable();
> + return ret;
> +}
> +
> int module_kallsyms_on_each_symbol(const char *modname,
> int (*fn)(void *, const char *,
> struct module *, unsigned long),
> --
> 2.39.2
>

--
Artem

2023-04-05 00:23:37

by patchwork-bot+netdevbpf

Subject: Re: [PATCH bpf-next] kallsyms: Disable preemption for find_kallsyms_symbol_value

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Andrii Nakryiko <[email protected]>:

On Tue, 4 Apr 2023 00:02:54 +0200 you wrote:
> Artem reported suspicious RCU usage [1]. The reason is that verifier
> calls find_kallsyms_symbol_value with preemption enabled which will
> trigger suspicious RCU usage warning in rcu_dereference_sched call.
>
> Disabling preemption in find_kallsyms_symbol_value and adding
> __find_kallsyms_symbol_value function.
>
> [...]

Here is the summary with links:
- [bpf-next] kallsyms: Disable preemption for find_kallsyms_symbol_value
https://git.kernel.org/bpf/bpf-next/c/d099f594ad56

You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

2023-04-06 14:57:21

by Petr Mladek

Subject: Re: [PATCH bpf-next] kallsyms: Disable preemption for find_kallsyms_symbol_value

On Tue 2023-04-04 00:02:54, Jiri Olsa wrote:
> Artem reported suspicious RCU usage [1]. The reason is that verifier
> calls find_kallsyms_symbol_value with preemption enabled which will
> trigger suspicious RCU usage warning in rcu_dereference_sched call.
>
> Disabling preemption in find_kallsyms_symbol_value and adding
> __find_kallsyms_symbol_value function.
>
> Fixes: 31bf1dbccfb0 ("bpf: Fix attaching fentry/fexit/fmod_ret/lsm to modules")
> [1] https://lore.kernel.org/bpf/[email protected]/
> Reported-by: Artem Savkov <[email protected]>
> Signed-off-by: Jiri Olsa <[email protected]>

Just for record:

Reviewed-by: Petr Mladek <[email protected]>

Best Regards,
Petr

2023-04-06 15:01:48

by Aaron Tomlin

Subject: Re: [PATCH bpf-next] kallsyms: Disable preemption for find_kallsyms_symbol_value

On Tue, Apr 04, 2023 at 12:02:54AM +0200, Jiri Olsa wrote:
> Artem reported suspicious RCU usage [1]. The reason is that verifier
> calls find_kallsyms_symbol_value with preemption enabled which will
> trigger suspicious RCU usage warning in rcu_dereference_sched call.
>
> Disabling preemption in find_kallsyms_symbol_value and adding
> __find_kallsyms_symbol_value function.
>
> Fixes: 31bf1dbccfb0 ("bpf: Fix attaching fentry/fexit/fmod_ret/lsm to modules")
> [1] https://lore.kernel.org/bpf/[email protected]/
> Reported-by: Artem Savkov <[email protected]>
> Signed-off-by: Jiri Olsa <[email protected]>
> ---
> kernel/module/kallsyms.c | 16 +++++++++++++---
> 1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
> index ab2376a1be88..bdc911dbcde5 100644
> --- a/kernel/module/kallsyms.c
> +++ b/kernel/module/kallsyms.c
> @@ -442,7 +442,7 @@ int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
> }
>
> /* Given a module and name of symbol, find and return the symbol's value */
> -unsigned long find_kallsyms_symbol_value(struct module *mod, const char *name)
> +static unsigned long __find_kallsyms_symbol_value(struct module *mod, const char *name)
> {
> unsigned int i;
> struct mod_kallsyms *kallsyms = rcu_dereference_sched(mod->kallsyms);
> @@ -466,7 +466,7 @@ static unsigned long __module_kallsyms_lookup_name(const char *name)
> if (colon) {
> mod = find_module_all(name, colon - name, false);
> if (mod)
> - return find_kallsyms_symbol_value(mod, colon + 1);
> + return __find_kallsyms_symbol_value(mod, colon + 1);
> return 0;
> }
>
> @@ -475,7 +475,7 @@ static unsigned long __module_kallsyms_lookup_name(const char *name)
>
> if (mod->state == MODULE_STATE_UNFORMED)
> continue;
> - ret = find_kallsyms_symbol_value(mod, name);
> + ret = __find_kallsyms_symbol_value(mod, name);
> if (ret)
> return ret;
> }
> @@ -494,6 +494,16 @@ unsigned long module_kallsyms_lookup_name(const char *name)
> return ret;
> }
>
> +unsigned long find_kallsyms_symbol_value(struct module *mod, const char *name)
> +{
> + unsigned long ret;
> +
> + preempt_disable();
> + ret = __find_kallsyms_symbol_value(mod, name);
> + preempt_enable();
> + return ret;
> +}
> +
> int module_kallsyms_on_each_symbol(const char *modname,
> int (*fn)(void *, const char *,
> struct module *, unsigned long),
> --
> 2.39.2
>

Reviewed-by: Aaron Tomlin <[email protected]>

--
Aaron Tomlin