[klibc] [PATCH] : store 4 bytes in arm64 errno

[Greg Thelen]

The arm64 post-syscall code (below) checks the syscall retval (x0) and
conditionally sets errno:

__syscall_common:
        cmp     x0, #0x0
        b.ge    2f
        neg     x0, x0
        ldr     x8, 1f
        str     x0, [x8]
        mov     x0, #-1
2:
        ret
1:
        .dword  errno

There is a bug. When the syscall returns a negative value "str x0, [x8]"
stores 8 bytes in the 4 byte errno. The 4 bytes that follow errno are
clobbered, which depending on linker data placement can corrupt
important process memory.

Only store 4 bytes in errno to avoid corruption.

Fixes: e4a2c914446b ("[klibc] arm64: Add arm64 support")
Signed-off-by: Greg Thelen <gthelen at google.com>
---
 usr/klibc/arch/arm64/syscall.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/usr/klibc/arch/arm64/syscall.S b/usr/klibc/arch/arm64/syscall.S
index 3ce91fb77aa5..e1004122577d 100644
--- a/usr/klibc/arch/arm64/syscall.S
+++ b/usr/klibc/arch/arm64/syscall.S
@@ -17,7 +17,7 @@ __syscall_common:
 	b.ge	2f
 	neg	x0, x0
 	ldr	x8, 1f
-	str	x0, [x8]
+	str	w0, [x8]
 	mov	x0, #-1
 2:
 	ret
-- 
2.37.1.595.g718a3a8f04-goog