2021-03-04 05:59:47

by Tiezhu Yang

Subject: [PATCH] riscv: Return -EFAULT if copy_to_user() failed in signal.c

copy_to_user() returns the amount left to copy, it should return -EFAULT
if copy to user failed.

Signed-off-by: Tiezhu Yang <[email protected]>
---
arch/riscv/kernel/signal.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c
index 65942b3..2238fc5 100644
--- a/arch/riscv/kernel/signal.c
+++ b/arch/riscv/kernel/signal.c
@@ -67,7 +67,7 @@ static long save_fp_state(struct pt_regs *regs,
fstate_save(current, regs);
err = __copy_to_user(state, &current->thread.fstate, sizeof(*state));
if (unlikely(err))
- return err;
+ return -EFAULT;

/* We support no other extension state at this time. */
for (i = 0; i < ARRAY_SIZE(sc_fpregs->q.reserved); i++) {
@@ -140,8 +140,12 @@ static long setup_sigcontext(struct rt_sigframe __user *frame,
{
struct sigcontext __user *sc = &frame->uc.uc_mcontext;
long err;
+
/* sc_regs is structured the same as the start of pt_regs */
err = __copy_to_user(&sc->sc_regs, regs, sizeof(sc->sc_regs));
+ if (unlikely(err))
+ return -EFAULT;
+
/* Save the floating-point state. */
if (has_fpu)
err |= save_fp_state(regs, &sc->sc_fpregs);
--
2.1.0

2021-03-04 06:11:11

by Ben Dooks

Subject: Re: [PATCH] riscv: Return -EFAULT if copy_to_user() failed in signal.c

On 02/03/2021 07:28, Tiezhu Yang wrote:
> copy_to_user() returns the amount left to copy, it should return -EFAULT
> if copy to user failed.

This looks technically correct, but the caller (only one)
will check for non-zero and will covert that to -EFAULT
in setup_rt_frame().

I expect if this change is done, it also needs to be done
for the callers too and there's a few others than assume
!=0 is an error.

I think it would be easier to define save_fp_state() to
return non-zero on error and note it does not return an
error code. It may be worth exiting the functio nif
the first __copy_to_user fails?

Note: setup_rt_frame -> setup_sigcontext -> save_fp_frame

>
> Signed-off-by: Tiezhu Yang <[email protected]>
> ---
> arch/riscv/kernel/signal.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c
> index 65942b3..2238fc5 100644
> --- a/arch/riscv/kernel/signal.c
> +++ b/arch/riscv/kernel/signal.c
> @@ -67,7 +67,7 @@ static long save_fp_state(struct pt_regs *regs,
> fstate_save(current, regs);
> err = __copy_to_user(state, &current->thread.fstate, sizeof(*state));
> if (unlikely(err))
> - return err;
> + return -EFAULT;
>
> /* We support no other extension state at this time. */
> for (i = 0; i < ARRAY_SIZE(sc_fpregs->q.reserved); i++) {
> @@ -140,8 +140,12 @@ static long setup_sigcontext(struct rt_sigframe __user *frame,
> {
> struct sigcontext __user *sc = &frame->uc.uc_mcontext;
> long err;
> +
> /* sc_regs is structured the same as the start of pt_regs */
> err = __copy_to_user(&sc->sc_regs, regs, sizeof(sc->sc_regs));
> + if (unlikely(err))
> + return -EFAULT;
> +
> /* Save the floating-point state. */
> if (has_fpu)
> err |= save_fp_state(regs, &sc->sc_fpregs);
>


--
Ben Dooks http://www.codethink.co.uk/
Senior Engineer Codethink - Providing Genius

https://www.codethink.co.uk/privacy.html

2021-03-04 08:09:38

by Tiezhu Yang

Subject: Re: [PATCH] riscv: Return -EFAULT if copy_to_user() failed in signal.c

On 03/02/2021 06:01 PM, Ben Dooks wrote:
> On 02/03/2021 07:28, Tiezhu Yang wrote:
>> copy_to_user() returns the amount left to copy, it should return -EFAULT
>> if copy to user failed.
>
> This looks technically correct, but the caller (only one)
> will check for non-zero and will covert that to -EFAULT
> in setup_rt_frame().

Yes, as you said, the original code logic has no problem, it will covert
that to -EFAULT in setup_rt_frame().

The initial aim of this patch is to make save_fp_state() return error code
if __copy_to_user() failed, just like it returns -EFAULT if __put_user()
failed.

I notice that restore_fp_state() has similar issue, it will return -EFAULT
if __get_user() failed and maybe return -EINVAL in the other error case,
both -EFAULT and -EINVAL are error code, but when __copy_from_user() failed,
it does not return an error code, which seems not so consistent.

>
> I expect if this change is done, it also needs to be done
> for the callers too and there's a few others than assume
> !=0 is an error.
>
> I think it would be easier to define save_fp_state() to
> return non-zero on error and note it does not return an
> error code. It may be worth exiting the functio nif
> the first __copy_to_user fails?

Now,
(1) is it necessary to do some changes? If yes, I will send v2 later.
Like this:

[PATCH v2] riscv: Return -EFAULT if copy_{to,from}_user() failed in
signal.c

copy_{to,from}_user() returns the amount left to copy, it should return
-EFAULT error code if copy {to,from} user failed, just like the return
value is an error code when {put,get}_user() failed, this is to make the
return value consistent, no function change.

Signed-off-by: Tiezhu Yang <[email protected]>
---
arch/riscv/kernel/signal.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c
index 65942b3..c76d877 100644
--- a/arch/riscv/kernel/signal.c
+++ b/arch/riscv/kernel/signal.c
@@ -39,7 +39,7 @@ static long restore_fp_state(struct pt_regs *regs,

err = __copy_from_user(&current->thread.fstate, state,
sizeof(*state));
if (unlikely(err))
- return err;
+ return -EFAULT;

fstate_restore(current, regs);

@@ -67,7 +67,7 @@ static long save_fp_state(struct pt_regs *regs,
fstate_save(current, regs);
err = __copy_to_user(state, &current->thread.fstate, sizeof(*state));
if (unlikely(err))
- return err;
+ return -EFAULT;

/* We support no other extension state at this time. */
for (i = 0; i < ARRAY_SIZE(sc_fpregs->q.reserved); i++) {
@@ -87,8 +87,12 @@ static long restore_sigcontext(struct pt_regs *regs,
struct sigcontext __user *sc)
{
long err;
+
/* sc_regs is structured the same as the start of pt_regs */
err = __copy_from_user(regs, &sc->sc_regs, sizeof(sc->sc_regs));
+ if (unlikely(err))
+ return -EFAULT;
+
/* Restore the floating-point state. */
if (has_fpu)
err |= restore_fp_state(regs, &sc->sc_fpregs);
@@ -140,8 +144,12 @@ static long setup_sigcontext(struct rt_sigframe
__user *frame,
{
struct sigcontext __user *sc = &frame->uc.uc_mcontext;
long err;
+
/* sc_regs is structured the same as the start of pt_regs */
err = __copy_to_user(&sc->sc_regs, regs, sizeof(sc->sc_regs));
+ if (unlikely(err))
+ return -EFAULT;
+
/* Save the floating-point state. */
if (has_fpu)
err |= save_fp_state(regs, &sc->sc_fpregs);
--
2.1.0

(2) or just leave it as it is and ignore this patch?

Thanks,
Tiezhu

>
> Note: setup_rt_frame -> setup_sigcontext -> save_fp_frame
>
>>
>> Signed-off-by: Tiezhu Yang <[email protected]>
>> ---
>> arch/riscv/kernel/signal.c | 6 +++++-
>> 1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c
>> index 65942b3..2238fc5 100644
>> --- a/arch/riscv/kernel/signal.c
>> +++ b/arch/riscv/kernel/signal.c
>> @@ -67,7 +67,7 @@ static long save_fp_state(struct pt_regs *regs,
>> fstate_save(current, regs);
>> err = __copy_to_user(state, &current->thread.fstate,
>> sizeof(*state));
>> if (unlikely(err))
>> - return err;
>> + return -EFAULT;
>> /* We support no other extension state at this time. */
>> for (i = 0; i < ARRAY_SIZE(sc_fpregs->q.reserved); i++) {
>> @@ -140,8 +140,12 @@ static long setup_sigcontext(struct rt_sigframe
>> __user *frame,
>> {
>> struct sigcontext __user *sc = &frame->uc.uc_mcontext;
>> long err;
>> +
>> /* sc_regs is structured the same as the start of pt_regs */
>> err = __copy_to_user(&sc->sc_regs, regs, sizeof(sc->sc_regs));
>> + if (unlikely(err))
>> + return -EFAULT;
>> +
>> /* Save the floating-point state. */
>> if (has_fpu)
>> err |= save_fp_state(regs, &sc->sc_fpregs);
>>
>
>