Re: [PATCH v2 2/3] arm64: syscall.h: Add sign extension handling in syscall_get_return_value for compat

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(a)arm.com&gt; Signed-off-by: He Zhe <zhe.he(a)windriver.com&gt; --- 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;