arm64: compat: Avoid sending SIGILL for unallocated syscall numbers

commit 169113ece0f29ebe884a6cfcf57c1ace04d8a36a upstream.

The ARM Linux kernel handles the EABI syscall numbers as follows:

  0           - NR_SYSCALLS-1	: Invoke syscall via syscall table
  NR_SYSCALLS - 0xeffff		: -ENOSYS (to be allocated in future)
  0xf0000     - 0xf07ff		: Private syscall or -ENOSYS if not allocated
  > 0xf07ff			: SIGILL

Our compat code gets this wrong and ends up sending SIGILL in response
to all syscalls greater than NR_SYSCALLS which have a value greater
than 0x7ff in the bottom 16 bits.

Fix this by defining the end of the ARM private syscall region and
checking the syscall number against that directly. Update the comment
while we're at it.

Cc: <stable@vger.kernel.org>
Cc: Dave Martin <Dave.Martin@arm.com>
Reported-by: Pi-Hsun Shih <pihsun@chromium.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h
index e0d0f5b856e74589404de44c8ca4323e454973ec..d52051879ffe2eef8bebb84d1856e7b0cb114245 100644 (file)
--- a/arch/arm64/include/asm/unistd.h
+++ b/arch/arm64/include/asm/unistd.h
@@ -40,8 +40,9 @@
  * The following SVCs are ARM private.
  */
 #define __ARM_NR_COMPAT_BASE           0x0f0000
-#define __ARM_NR_compat_cacheflush     (__ARM_NR_COMPAT_BASE+2)
-#define __ARM_NR_compat_set_tls                (__ARM_NR_COMPAT_BASE+5)
+#define __ARM_NR_compat_cacheflush     (__ARM_NR_COMPAT_BASE + 2)
+#define __ARM_NR_compat_set_tls                (__ARM_NR_COMPAT_BASE + 5)
+#define __ARM_NR_COMPAT_END            (__ARM_NR_COMPAT_BASE + 0x800)
 
 #define __NR_compat_syscalls           399
 #endif

diff --git a/arch/arm64/kernel/sys_compat.c b/arch/arm64/kernel/sys_compat.c
index a6109825eeb97133b8cbccc9a7fe98d2f11f14e4..7be666062c7c5e9fbb29eeb02284390cad0ee821 100644 (file)
--- a/arch/arm64/kernel/sys_compat.c
+++ b/arch/arm64/kernel/sys_compat.c
@@ -102,12 +102,12 @@ long compat_arm_syscall(struct pt_regs *regs)
 
        default:
                /*
-                * Calls 9f00xx..9f07ff are defined to return -ENOSYS
+                * Calls 0xf0xxx..0xf07ff are defined to return -ENOSYS
                 * if not implemented, rather than raising SIGILL. This
                 * way the calling program can gracefully determine whether
                 * a feature is supported.
                 */
-               if ((no & 0xffff) <= 0x7ff)
+               if (no < __ARM_NR_COMPAT_END)
                        return -ENOSYS;
                break;
        }