| Message ID | 20210416075533.7720-2-zhe.he@windriver.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/3] arm64: ptrace: Add is_syscall_success to handle compat | expand |
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 <zhe.he@windriver.com> > --- > 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 <zhe.he@windriver.com> > > --- > > 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 > >
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,
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 <zhe.he@windriver.com> --- arch/arm64/include/asm/syscall.h | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)