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authorWill Deacon <will@kernel.org>2020-07-03 12:08:42 +0100
committerWill Deacon <will@kernel.org>2020-07-16 11:41:31 +0100
commit15956689a0e60aa0c795174f3c310b60d8794235 (patch)
tree7e7e6e911ca9ccbf33c0db2aaa54be3b59e022da /arch/arm64/include
parent3a5a4366cecc25daa300b9a9174f7fdd352b9068 (diff)
downloadlinux-15956689a0e60aa0c795174f3c310b60d8794235.tar.bz2
arm64: compat: Ensure upper 32 bits of x0 are zero on syscall return
Although we zero the upper bits of x0 on entry to the kernel from an AArch32 task, we do not clear them on the exception return path and can therefore expose 64-bit sign extended syscall return values to userspace via interfaces such as the 'perf_regs' ABI, which deal exclusively with 64-bit registers. Explicitly clear the upper 32 bits of x0 on return from a compat system call. Cc: <stable@vger.kernel.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Keno Fischer <keno@juliacomputing.com> Cc: Luis Machado <luis.machado@linaro.org> Signed-off-by: Will Deacon <will@kernel.org>
Diffstat (limited to 'arch/arm64/include')
-rw-r--r--arch/arm64/include/asm/syscall.h12
1 files changed, 11 insertions, 1 deletions
diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h
index 65299a2dcf9c..cfc0672013f6 100644
--- a/arch/arm64/include/asm/syscall.h
+++ b/arch/arm64/include/asm/syscall.h
@@ -34,6 +34,10 @@ static inline long syscall_get_error(struct task_struct *task,
struct pt_regs *regs)
{
unsigned long error = regs->regs[0];
+
+ if (is_compat_thread(task_thread_info(task)))
+ error = sign_extend64(error, 31);
+
return IS_ERR_VALUE(error) ? error : 0;
}
@@ -47,7 +51,13 @@ static inline void syscall_set_return_value(struct task_struct *task,
struct pt_regs *regs,
int error, long val)
{
- regs->regs[0] = (long) error ? error : val;
+ if (error)
+ val = error;
+
+ if (is_compat_thread(task_thread_info(task)))
+ val = lower_32_bits(val);
+
+ regs->regs[0] = val;
}
#define SYSCALL_MAX_ARGS 6