| Message ID | 20210423103533.30121-2-zhe.he@windriver.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2,1/3] arm64: ptrace: Add is_syscall_success to handle compat | expand |
Hi, On Fri, Apr 23, 2021 at 06:35:32PM +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. > > Suggested-by: Mark Rutland <mark.rutland@arm.com> > Signed-off-by: He Zhe <zhe.he@windriver.com> > --- > v1 to v2: Improve error code check suggested by Mark > > arch/arm64/include/asm/syscall.h | 15 ++++++++++++++- > 1 file changed, 14 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h > index cfc0672013f6..c3b5fca82ff4 100644 > --- a/arch/arm64/include/asm/syscall.h > +++ b/arch/arm64/include/asm/syscall.h > @@ -44,7 +44,20 @@ 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]; > + long error = val; > + > + if (compat_user_mode(regs)) > + error = sign_extend64(error, 31); > + > + /* > + * Return codes with bit 31 set may or may not be an error code. > + * For example, mmap may return a legal 32 bit address with bit 31 set > + * for 32 bit thread, in which case the untouched val should be > + * returned. Otherwise, the sign-extended error should be returned if > + * it still falls in error number range. > + */ > + return IS_ERR_VALUE(error) ? error : val; I'm afraid I have misled you here. I wrote up a test that uses PTRACE_GET_SYSCALL_INFO, and I found that on a 32-bit arm (v5.12) kernel, *all* syscall return values get sign-extended after all. For example, if (on a 32-bit kernel) I use MAP_FIXED to mmap() at address 0x8bad0000, the return value reported in ptrace_syscall_info::exit::rval is 0xffffffff8bad0000. So for that we shoudn't have the IS_ERR_VALUE() check after all, but I'm not currently sure whether there are other cases where 32-bit arm wouldn't sign-extend, and I think we'll need to dig into this some more. Thanks, Mark.
diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h index cfc0672013f6..c3b5fca82ff4 100644 --- a/arch/arm64/include/asm/syscall.h +++ b/arch/arm64/include/asm/syscall.h @@ -44,7 +44,20 @@ 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]; + long error = val; + + if (compat_user_mode(regs)) + error = sign_extend64(error, 31); + + /* + * Return codes with bit 31 set may or may not be an error code. + * For example, mmap may return a legal 32 bit address with bit 31 set + * for 32 bit thread, in which case the untouched val should be + * returned. Otherwise, the sign-extended error should be returned if + * it still falls in error number range. + */ + return IS_ERR_VALUE(error) ? error : 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. Suggested-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: He Zhe <zhe.he@windriver.com> --- v1 to v2: Improve error code check suggested by Mark arch/arm64/include/asm/syscall.h | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-)