On Thu, Jan 03, 2019 at 06:13:58PM +0000, Will Deacon wrote:
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
arch/arm64/include/asm/unistd.h | 5 +++-- arch/arm64/kernel/sys_compat.c | 4 ++-- 2 files changed, 5 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h index b13ca091f833..be66a54ee3a1 100644 --- 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_syscall_end (__ARM_NR_COMPAT_BASE + 0x800)
Nit: there is no compat_syscall_end(). Can we make this #define upper case, like __ARM_NR_COMPAT_BASE, since a symbolic bound, not a syscall number?
It would be nice to have this for arch/arm too rather than the current magic numbers.
#define __NR_compat_syscalls 399 #endif diff --git a/arch/arm64/kernel/sys_compat.c b/arch/arm64/kernel/sys_compat.c index 32653d156747..5972b7533fa0 100644 --- 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_syscall_end)
arm_syscall() in arch/arm is not responsible for handling syscalls less __ARM_NR_BASE; the code in entry-common.S redirects those directly to sys_ni_syscall() instead.
Given how fiddly this is I think it's preferable if we keep to the arch/arm code structure as much as possible, and call this function only when no >= __ARM_NR_COMPAT_BASE?
Regular (possibly unallocated) Linux syscalls can be more naturally handled in do_ni_syscall() instead IMHO, mirroring the entry-common.S code that it replaces.
Cheers ---Dave