Add sign extension handling in syscall_get_return_value so that it can
handle 32-bit compatible case and can be used by for example audit, just
like what syscall_get_error does.
Signed-off-by: He Zhe <[email protected]>
---
arch/arm64/include/asm/syscall.h | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h
index cfc0672013f6..cd7a22787aeb 100644
--- a/arch/arm64/include/asm/syscall.h
+++ b/arch/arm64/include/asm/syscall.h
@@ -44,7 +44,12 @@ static inline long syscall_get_error(struct task_struct *task,
static inline long syscall_get_return_value(struct task_struct *task,
struct pt_regs *regs)
{
- return regs->regs[0];
+ long val = regs->regs[0];
+
+ if (is_compat_thread(task_thread_info(task)))
+ val = sign_extend64(val, 31);
+
+ return val;
}
static inline void syscall_set_return_value(struct task_struct *task,
--
2.17.1
On 04/16, He Zhe wrote:
>
> --- a/arch/arm64/include/asm/syscall.h
> +++ b/arch/arm64/include/asm/syscall.h
> @@ -44,7 +44,12 @@ static inline long syscall_get_error(struct task_struct *task,
> static inline long syscall_get_return_value(struct task_struct *task,
> struct pt_regs *regs)
> {
> - return regs->regs[0];
> + long val = regs->regs[0];
> +
> + if (is_compat_thread(task_thread_info(task)))
> + val = sign_extend64(val, 31);
> +
> + return val;
> }
I can't really review these arm-specific patches, but with this change both
syscall_get_error() and is_syscall_success() can use syscall_get_return_value()
to avoid the code duplication.
Oleg.
On 4/16/21 5:43 PM, Oleg Nesterov wrote:
> On 04/16, He Zhe wrote:
>> --- a/arch/arm64/include/asm/syscall.h
>> +++ b/arch/arm64/include/asm/syscall.h
>> @@ -44,7 +44,12 @@ static inline long syscall_get_error(struct task_struct *task,
>> static inline long syscall_get_return_value(struct task_struct *task,
>> struct pt_regs *regs)
>> {
>> - return regs->regs[0];
>> + long val = regs->regs[0];
>> +
>> + if (is_compat_thread(task_thread_info(task)))
>> + val = sign_extend64(val, 31);
>> +
>> + return val;
>> }
> I can't really review these arm-specific patches, but with this change both
> syscall_get_error() and is_syscall_success() can use syscall_get_return_value()
> to avoid the code duplication.
Thanks. I'll improve this if v2 is needed.
Regards,
Zhe
>
> Oleg.
>
On Fri, Apr 16, 2021 at 03:55:32PM +0800, He Zhe wrote:
> Add sign extension handling in syscall_get_return_value so that it can
> handle 32-bit compatible case and can be used by for example audit, just
> like what syscall_get_error does.
If a compat syscall can ever legitimately return a non-error value with
bit 31 set, and this sign-extends it, is that ever going to reach
userspace as a 64-bit value?
IIUC things like mmap() can return pointers above 2GiB for a compat
task, so I'm a bit uneasy that we'd handle those wrong. I can't see a
way of preventing that unless we keep the upper 32 bits for errors.
Mark.
>
> Signed-off-by: He Zhe <[email protected]>
> ---
> arch/arm64/include/asm/syscall.h | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h
> index cfc0672013f6..cd7a22787aeb 100644
> --- a/arch/arm64/include/asm/syscall.h
> +++ b/arch/arm64/include/asm/syscall.h
> @@ -44,7 +44,12 @@ static inline long syscall_get_error(struct task_struct *task,
> static inline long syscall_get_return_value(struct task_struct *task,
> struct pt_regs *regs)
> {
> - return regs->regs[0];
> + long val = regs->regs[0];
> +
> + if (is_compat_thread(task_thread_info(task)))
> + val = sign_extend64(val, 31);
> +
> + return val;
> }
>
> static inline void syscall_set_return_value(struct task_struct *task,
> --
> 2.17.1
>
On Wed, Apr 21, 2021 at 06:41:05PM +0100, Mark Rutland wrote:
> On Fri, Apr 16, 2021 at 03:55:32PM +0800, He Zhe wrote:
> > Add sign extension handling in syscall_get_return_value so that it can
> > handle 32-bit compatible case and can be used by for example audit, just
> > like what syscall_get_error does.
>
> If a compat syscall can ever legitimately return a non-error value with
> bit 31 set, and this sign-extends it, is that ever going to reach
> userspace as a 64-bit value?
>
> IIUC things like mmap() can return pointers above 2GiB for a compat
> task, so I'm a bit uneasy that we'd handle those wrong. I can't see a
> way of preventing that unless we keep the upper 32 bits for errors.
Looking at this with fresh eyes, I think we can more closely mirror
syscall_get_error(), and do something like:
static inline long syscall_get_return_value(struct task_struct *task,
struct pt_regs *regs)
{
long val = regs->regs[0];
long error = val;
if (is_compat_thread(task_thread_info(task)))
error = sign_extend64(error, 31);
return IS_ERR_VALUE(error) ? error : val;
}
Thanks,
Mark.
>
> Mark.
>
> >
> > Signed-off-by: He Zhe <[email protected]>
> > ---
> > arch/arm64/include/asm/syscall.h | 7 ++++++-
> > 1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h
> > index cfc0672013f6..cd7a22787aeb 100644
> > --- a/arch/arm64/include/asm/syscall.h
> > +++ b/arch/arm64/include/asm/syscall.h
> > @@ -44,7 +44,12 @@ static inline long syscall_get_error(struct task_struct *task,
> > static inline long syscall_get_return_value(struct task_struct *task,
> > struct pt_regs *regs)
> > {
> > - return regs->regs[0];
> > + long val = regs->regs[0];
> > +
> > + if (is_compat_thread(task_thread_info(task)))
> > + val = sign_extend64(val, 31);
> > +
> > + return val;
> > }
> >
> > static inline void syscall_set_return_value(struct task_struct *task,
> > --
> > 2.17.1
> >