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[PATCH] riscv: ftrace: Properly acquire text_mutex to fix a race condition

Alexandre Ghiti posted 1 patch 3 months ago
There is a newer version of this series
arch/riscv/kernel/ftrace.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
[PATCH] riscv: ftrace: Properly acquire text_mutex to fix a race condition
Posted by Alexandre Ghiti 3 months ago 
As reported by lockdep, some patching was done without acquiring
text_mutex, so there could be a race when mapping the page to patch
since we use the same fixmap entry.

Reported-by: Han Gao <rabenda.cn@gmail.com>
Reported-by: Vivian Wang <wangruikang@iscas.ac.cn>
Reported-by: Yao Zi <ziyao@disroot.org>
Closes: https://lore.kernel.org/linux-riscv/aGODMpq7TGINddzM@pie.lan/
Tested-by: Yao Zi <ziyao@disroot.org>
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
---
 arch/riscv/kernel/ftrace.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index 4c6c24380cfd9d6c51f0e4340cd674160b83a610..22e7bdf8de2b6ca950cf2c8b734bc82ea46ba8bf 100644
--- a/arch/riscv/kernel/ftrace.c
+++ b/arch/riscv/kernel/ftrace.c
@@ -14,6 +14,16 @@
 #include <asm/text-patching.h>
 
 #ifdef CONFIG_DYNAMIC_FTRACE
+void ftrace_arch_code_modify_prepare(void)
+{
+	mutex_lock(&text_mutex);
+}
+
+void ftrace_arch_code_modify_post_process(void)
+{
+	mutex_unlock(&text_mutex);
+}
+
 unsigned long ftrace_call_adjust(unsigned long addr)
 {
 	if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS))
@@ -29,10 +39,8 @@ unsigned long arch_ftrace_get_symaddr(unsigned long fentry_ip)
 
 void arch_ftrace_update_code(int command)
 {
-	mutex_lock(&text_mutex);
 	command |= FTRACE_MAY_SLEEP;
 	ftrace_modify_all_code(command);
-	mutex_unlock(&text_mutex);
 	flush_icache_all();
 }
 
@@ -149,6 +157,8 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
 	unsigned int nops[2], offset;
 	int ret;
 
+	guard(mutex)(&text_mutex);
+
 	ret = ftrace_rec_set_nop_ops(rec);
 	if (ret)
 		return ret;
@@ -157,9 +167,7 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
 	nops[0] = to_auipc_t0(offset);
 	nops[1] = RISCV_INSN_NOP4;
 
-	mutex_lock(&text_mutex);
 	ret = patch_insn_write((void *)pc, nops, 2 * MCOUNT_INSN_SIZE);
-	mutex_unlock(&text_mutex);
 
 	return ret;
 }

---
base-commit: d7b8f8e20813f0179d8ef519541a3527e7661d3a
change-id: 20250708-alex-fixes-1e719b9899f3

Best regards,
-- 
Alexandre Ghiti <alexghiti@rivosinc.com>
Re: [PATCH] riscv: ftrace: Properly acquire text_mutex to fix a race condition
Posted by Andy Chiu 2 months, 4 weeks ago 
On Tue, Jul 8, 2025 at 4:47 PM Alexandre Ghiti <alexghiti@rivosinc.com> wrote:
>
> As reported by lockdep, some patching was done without acquiring
> text_mutex, so there could be a race when mapping the page to patch
> since we use the same fixmap entry.
>
> Reported-by: Han Gao <rabenda.cn@gmail.com>
> Reported-by: Vivian Wang <wangruikang@iscas.ac.cn>
> Reported-by: Yao Zi <ziyao@disroot.org>
> Closes: https://lore.kernel.org/linux-riscv/aGODMpq7TGINddzM@pie.lan/
> Tested-by: Yao Zi <ziyao@disroot.org>
> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>

Reviewed-by: Andy Chiu <andybnac@gmail.com>

> ---
>  arch/riscv/kernel/ftrace.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
> index 4c6c24380cfd9d6c51f0e4340cd674160b83a610..22e7bdf8de2b6ca950cf2c8b734bc82ea46ba8bf 100644
> --- a/arch/riscv/kernel/ftrace.c
> +++ b/arch/riscv/kernel/ftrace.c
> @@ -14,6 +14,16 @@
>  #include <asm/text-patching.h>
>
>  #ifdef CONFIG_DYNAMIC_FTRACE
> +void ftrace_arch_code_modify_prepare(void)
> +{
> +       mutex_lock(&text_mutex);
> +}
> +
> +void ftrace_arch_code_modify_post_process(void)
> +{
> +       mutex_unlock(&text_mutex);
> +}
> +
>  unsigned long ftrace_call_adjust(unsigned long addr)
>  {
>         if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS))
> @@ -29,10 +39,8 @@ unsigned long arch_ftrace_get_symaddr(unsigned long fentry_ip)
>
>  void arch_ftrace_update_code(int command)
>  {
> -       mutex_lock(&text_mutex);
>         command |= FTRACE_MAY_SLEEP;
>         ftrace_modify_all_code(command);
> -       mutex_unlock(&text_mutex);
>         flush_icache_all();
>  }
>
> @@ -149,6 +157,8 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
>         unsigned int nops[2], offset;
>         int ret;
>
> +       guard(mutex)(&text_mutex);
> +
>         ret = ftrace_rec_set_nop_ops(rec);
>         if (ret)
>                 return ret;
> @@ -157,9 +167,7 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
>         nops[0] = to_auipc_t0(offset);
>         nops[1] = RISCV_INSN_NOP4;
>
> -       mutex_lock(&text_mutex);
>         ret = patch_insn_write((void *)pc, nops, 2 * MCOUNT_INSN_SIZE);
> -       mutex_unlock(&text_mutex);
>
>         return ret;
>  }
>
> ---
> base-commit: d7b8f8e20813f0179d8ef519541a3527e7661d3a
> change-id: 20250708-alex-fixes-1e719b9899f3
>
> Best regards,
> --
> Alexandre Ghiti <alexghiti@rivosinc.com>
>
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv
Re: [PATCH] riscv: ftrace: Properly acquire text_mutex to fix a race condition
Posted by Han Gao 2 months, 4 weeks ago 
On Tue, Jul 8, 2025 at 4:34 PM Alexandre Ghiti <alexghiti@rivosinc.com> wrote:
>
> As reported by lockdep, some patching was done without acquiring
> text_mutex, so there could be a race when mapping the page to patch
> since we use the same fixmap entry.
>
> Reported-by: Han Gao <rabenda.cn@gmail.com>
> Reported-by: Vivian Wang <wangruikang@iscas.ac.cn>
> Reported-by: Yao Zi <ziyao@disroot.org>
> Closes: https://lore.kernel.org/linux-riscv/aGODMpq7TGINddzM@pie.lan/
> Tested-by: Yao Zi <ziyao@disroot.org>
> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Tested-by: Han Gao <rabenda.cn@gmail.com>
> ---
>  arch/riscv/kernel/ftrace.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
> index 4c6c24380cfd9d6c51f0e4340cd674160b83a610..22e7bdf8de2b6ca950cf2c8b734bc82ea46ba8bf 100644
> --- a/arch/riscv/kernel/ftrace.c
> +++ b/arch/riscv/kernel/ftrace.c
> @@ -14,6 +14,16 @@
>  #include <asm/text-patching.h>
>
>  #ifdef CONFIG_DYNAMIC_FTRACE
> +void ftrace_arch_code_modify_prepare(void)
> +{
> +       mutex_lock(&text_mutex);
> +}
> +
> +void ftrace_arch_code_modify_post_process(void)
> +{
> +       mutex_unlock(&text_mutex);
> +}
> +
>  unsigned long ftrace_call_adjust(unsigned long addr)
>  {
>         if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS))
> @@ -29,10 +39,8 @@ unsigned long arch_ftrace_get_symaddr(unsigned long fentry_ip)
>
>  void arch_ftrace_update_code(int command)
>  {
> -       mutex_lock(&text_mutex);
>         command |= FTRACE_MAY_SLEEP;
>         ftrace_modify_all_code(command);
> -       mutex_unlock(&text_mutex);
>         flush_icache_all();
>  }
>
> @@ -149,6 +157,8 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
>         unsigned int nops[2], offset;
>         int ret;
>
> +       guard(mutex)(&text_mutex);
> +
>         ret = ftrace_rec_set_nop_ops(rec);
>         if (ret)
>                 return ret;
> @@ -157,9 +167,7 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
>         nops[0] = to_auipc_t0(offset);
>         nops[1] = RISCV_INSN_NOP4;
>
> -       mutex_lock(&text_mutex);
>         ret = patch_insn_write((void *)pc, nops, 2 * MCOUNT_INSN_SIZE);
> -       mutex_unlock(&text_mutex);
>
>         return ret;
>  }
>
> ---
> base-commit: d7b8f8e20813f0179d8ef519541a3527e7661d3a
> change-id: 20250708-alex-fixes-1e719b9899f3
>
> Best regards,
> --
> Alexandre Ghiti <alexghiti@rivosinc.com>
>
Re: [PATCH] riscv: ftrace: Properly acquire text_mutex to fix a race condition
Posted by Masami Hiramatsu (Google) 2 months, 4 weeks ago 
On Tue, 08 Jul 2025 08:33:48 +0000
Alexandre Ghiti <alexghiti@rivosinc.com> wrote:

> As reported by lockdep, some patching was done without acquiring
> text_mutex, so there could be a race when mapping the page to patch
> since we use the same fixmap entry.
> 
> Reported-by: Han Gao <rabenda.cn@gmail.com>
> Reported-by: Vivian Wang <wangruikang@iscas.ac.cn>
> Reported-by: Yao Zi <ziyao@disroot.org>
> Closes: https://lore.kernel.org/linux-riscv/aGODMpq7TGINddzM@pie.lan/
> Tested-by: Yao Zi <ziyao@disroot.org>
> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
> ---
>  arch/riscv/kernel/ftrace.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
> index 4c6c24380cfd9d6c51f0e4340cd674160b83a610..22e7bdf8de2b6ca950cf2c8b734bc82ea46ba8bf 100644
> --- a/arch/riscv/kernel/ftrace.c
> +++ b/arch/riscv/kernel/ftrace.c
> @@ -14,6 +14,16 @@
>  #include <asm/text-patching.h>
>  
>  #ifdef CONFIG_DYNAMIC_FTRACE
> +void ftrace_arch_code_modify_prepare(void)

To be sure this is acquire the text_mutex, add __acquires(&text_mutex) here.

> +{
> +	mutex_lock(&text_mutex);
> +}
> +
> +void ftrace_arch_code_modify_post_process(void)

Ditto, add __releases(&text_mutex) here.

others looks good to me.

Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Thanks,

> +{
> +	mutex_unlock(&text_mutex);
> +}
> +
>  unsigned long ftrace_call_adjust(unsigned long addr)
>  {
>  	if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS))
> @@ -29,10 +39,8 @@ unsigned long arch_ftrace_get_symaddr(unsigned long fentry_ip)
>  
>  void arch_ftrace_update_code(int command)
>  {
> -	mutex_lock(&text_mutex);
>  	command |= FTRACE_MAY_SLEEP;
>  	ftrace_modify_all_code(command);
> -	mutex_unlock(&text_mutex);
>  	flush_icache_all();
>  }
>  
> @@ -149,6 +157,8 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
>  	unsigned int nops[2], offset;
>  	int ret;
>  
> +	guard(mutex)(&text_mutex);
> +
>  	ret = ftrace_rec_set_nop_ops(rec);
>  	if (ret)
>  		return ret;
> @@ -157,9 +167,7 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
>  	nops[0] = to_auipc_t0(offset);
>  	nops[1] = RISCV_INSN_NOP4;
>  
> -	mutex_lock(&text_mutex);
>  	ret = patch_insn_write((void *)pc, nops, 2 * MCOUNT_INSN_SIZE);
> -	mutex_unlock(&text_mutex);
>  
>  	return ret;
>  }
> 
> ---
> base-commit: d7b8f8e20813f0179d8ef519541a3527e7661d3a
> change-id: 20250708-alex-fixes-1e719b9899f3
> 
> Best regards,
> -- 
> Alexandre Ghiti <alexghiti@rivosinc.com>
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>
Re: [PATCH] riscv: ftrace: Properly acquire text_mutex to fix a race condition
Posted by Palmer Dabbelt 3 months ago 
On Tue, 08 Jul 2025 01:33:48 PDT (-0700), alexghiti@rivosinc.com wrote:
> As reported by lockdep, some patching was done without acquiring
> text_mutex, so there could be a race when mapping the page to patch
> since we use the same fixmap entry.
>
> Reported-by: Han Gao <rabenda.cn@gmail.com>
> Reported-by: Vivian Wang <wangruikang@iscas.ac.cn>
> Reported-by: Yao Zi <ziyao@disroot.org>
> Closes: https://lore.kernel.org/linux-riscv/aGODMpq7TGINddzM@pie.lan/
> Tested-by: Yao Zi <ziyao@disroot.org>
> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
> ---
>  arch/riscv/kernel/ftrace.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
> index 4c6c24380cfd9d6c51f0e4340cd674160b83a610..22e7bdf8de2b6ca950cf2c8b734bc82ea46ba8bf 100644
> --- a/arch/riscv/kernel/ftrace.c
> +++ b/arch/riscv/kernel/ftrace.c
> @@ -14,6 +14,16 @@
>  #include <asm/text-patching.h>
>
>  #ifdef CONFIG_DYNAMIC_FTRACE
> +void ftrace_arch_code_modify_prepare(void)
> +{
> +	mutex_lock(&text_mutex);
> +}
> +
> +void ftrace_arch_code_modify_post_process(void)
> +{
> +	mutex_unlock(&text_mutex);
> +}

IIRC there's a reason we don't do it this way, we had (or had tried to) 
have it before.  It's been a while, though, and I'm just having some a 
coffee so may I'm just wrong...

>  unsigned long ftrace_call_adjust(unsigned long addr)
>  {
>  	if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS))
> @@ -29,10 +39,8 @@ unsigned long arch_ftrace_get_symaddr(unsigned long fentry_ip)
>
>  void arch_ftrace_update_code(int command)
>  {
> -	mutex_lock(&text_mutex);
>  	command |= FTRACE_MAY_SLEEP;
>  	ftrace_modify_all_code(command);
> -	mutex_unlock(&text_mutex);
>  	flush_icache_all();
>  }
>
> @@ -149,6 +157,8 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
>  	unsigned int nops[2], offset;
>  	int ret;
>
> +	guard(mutex)(&text_mutex);
> +
>  	ret = ftrace_rec_set_nop_ops(rec);
>  	if (ret)
>  		return ret;
> @@ -157,9 +167,7 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
>  	nops[0] = to_auipc_t0(offset);
>  	nops[1] = RISCV_INSN_NOP4;
>
> -	mutex_lock(&text_mutex);
>  	ret = patch_insn_write((void *)pc, nops, 2 * MCOUNT_INSN_SIZE);
> -	mutex_unlock(&text_mutex);
>
>  	return ret;
>  }
>
> ---
> base-commit: d7b8f8e20813f0179d8ef519541a3527e7661d3a
> change-id: 20250708-alex-fixes-1e719b9899f3
>
> Best regards,
Re: [PATCH] riscv: ftrace: Properly acquire text_mutex to fix a race condition
Posted by Steven Rostedt 2 months, 4 weeks ago 
On Wed, 09 Jul 2025 07:12:47 -0700 (PDT)
Palmer Dabbelt <palmer@dabbelt.com> wrote:

> >  #ifdef CONFIG_DYNAMIC_FTRACE
> > +void ftrace_arch_code_modify_prepare(void)
> > +{
> > +	mutex_lock(&text_mutex);
> > +}
> > +
> > +void ftrace_arch_code_modify_post_process(void)
> > +{
> > +	mutex_unlock(&text_mutex);
> > +}  
> 
> IIRC there's a reason we don't do it this way, we had (or had tried to) 
> have it before.  It's been a while, though, and I'm just having some a 
> coffee so may I'm just wrong...

Yes, because it caused issues with stop machine[1], but if you are no
longer using stop machine, this should be what you should do now.

[1] https://lore.kernel.org/all/20220310045454.672097-1-changbin.du@gmail.com/

-- Steve
Re: [PATCH] riscv: ftrace: Properly acquire text_mutex to fix a race condition
Posted by Palmer Dabbelt 2 months, 3 weeks ago 
On Wed, 09 Jul 2025 09:45:36 PDT (-0700), rostedt@goodmis.org wrote:
> On Wed, 09 Jul 2025 07:12:47 -0700 (PDT)
> Palmer Dabbelt <palmer@dabbelt.com> wrote:
>
>> >  #ifdef CONFIG_DYNAMIC_FTRACE
>> > +void ftrace_arch_code_modify_prepare(void)
>> > +{
>> > +	mutex_lock(&text_mutex);
>> > +}
>> > +
>> > +void ftrace_arch_code_modify_post_process(void)
>> > +{
>> > +	mutex_unlock(&text_mutex);
>> > +}
>>
>> IIRC there's a reason we don't do it this way, we had (or had tried to)
>> have it before.  It's been a while, though, and I'm just having some a
>> coffee so may I'm just wrong...
>
> Yes, because it caused issues with stop machine[1], but if you are no
> longer using stop machine, this should be what you should do now.
>
> [1] https://lore.kernel.org/all/20220310045454.672097-1-changbin.du@gmail.com/

Thanks.  The v2 staged for the tester, should show up on fixes soon.

>
> -- Steve

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