On Fri, Aug 12, 2011 at 5:01 PM, Sergei Trofimovich <slyfox@xxxxxxxxxx> wrote:
> The bug was accidentally found by the following program:
> #include <asm/sysinfo.h>
> #include <asm/unistd.h>
> #include <sys/syscall.h>
> static int setsysinfo(unsigned long op, void *buffer, unsigned long size,
> int *start, void *arg, unsigned long flag) {
> return syscall(__NR_osf_setsysinfo, op, buffer, size, start, arg, flag);
> }
>
> int main(int argc, char **argv) {
> short x[10];
> unsigned int buf[2] = { SSIN_UACPROC, UAC_SIGBUS, };
> setsysinfo(SSI_NVPAIRS, buf, 1, 0, 0, 0);
>
> int *y = (int*) (x+1);
> *y = 0;
> return 0;
> }
>
> The program shoud fail on SIGBUS, but didn't.
>
> The patch is a second part of userspace flag fix:
>> commit 745dd2405e281d96c0a449103bdf6a895048f28c
>> Author: Michael Cree <mcree@xxxxxxxxxxxx>
>> Date: Mon Nov 30 22:44:40 2009 -0500
>>
>> Alpha: Rearrange thread info flags fixing two regressions
>>
>> Both regressions fixed by (1) rearranging TIF_NOTIFY_RESUME flag to be
>> in lower 8 bits of the thread info flags, and (2) making sure that
>> ALPHA_UAC_SHIFT matches the rearrangement of the thread info flags.
>
> Deleted outdated out-of-sync 'UAC_SHIFT' (the cause of bug) in favour of 'ALPHA_UAC_SHIFT'.
>
> Signed-off-by: Sergei Trofimovich <slyfox@xxxxxxxxxx>
> Cc: linux-alpha@xxxxxxxxxxxxxxx
> Cc: Michael Cree <mcree@xxxxxxxxxxxx>
> Cc: Richard Henderson <rth@xxxxxxxxxxx>
> Cc: Ivan Kokshaysky <ink@xxxxxxxxxxxxxxxxxxxx>
> Cc: Matt Turner <mattst88@xxxxxxxxx>
> ---
> arch/alpha/include/asm/sysinfo.h | 9 ---------
> arch/alpha/include/asm/thread_info.h | 8 ++++----
> arch/alpha/kernel/osf_sys.c | 7 ++++---
> 3 files changed, 8 insertions(+), 16 deletions(-)
>
> diff --git a/arch/alpha/include/asm/sysinfo.h b/arch/alpha/include/asm/sysinfo.h
> index 086aba2..e77d77c 100644
> --- a/arch/alpha/include/asm/sysinfo.h
> +++ b/arch/alpha/include/asm/sysinfo.h
> @@ -27,13 +27,4 @@
> #define UAC_NOFIX 2
> #define UAC_SIGBUS 4
>
> -
> -#ifdef __KERNEL__
> -
> -/* This is the shift that is applied to the UAC bits as stored in the
> - per-thread flags. See thread_info.h. */
> -#define UAC_SHIFT 6
> -
> -#endif
> -
> #endif /* __ASM_ALPHA_SYSINFO_H */
> diff --git a/arch/alpha/include/asm/thread_info.h b/arch/alpha/include/asm/thread_info.h
> index 6f32f9c..ff73db0 100644
> --- a/arch/alpha/include/asm/thread_info.h
> +++ b/arch/alpha/include/asm/thread_info.h
> @@ -74,9 +74,9 @@ register struct thread_info *__current_thread_info __asm__("$8");
> #define TIF_NEED_RESCHED 3 /* rescheduling necessary */
> #define TIF_POLLING_NRFLAG 8 /* poll_idle is polling NEED_RESCHED */
> #define TIF_DIE_IF_KERNEL 9 /* dik recursion lock */
> -#define TIF_UAC_NOPRINT 10 /* see sysinfo.h */
> -#define TIF_UAC_NOFIX 11
> -#define TIF_UAC_SIGBUS 12
> +#define TIF_UAC_NOPRINT 10 /* ! Preserve sequence of following */
> +#define TIF_UAC_NOFIX 11 /* ! flags as they match */
> +#define TIF_UAC_SIGBUS 12 /* ! userspace part of 'osf_sysinfo' */
> #define TIF_MEMDIE 13 /* is terminating due to OOM killer */
> #define TIF_RESTORE_SIGMASK 14 /* restore signal mask in do_signal */
> #define TIF_FREEZE 16 /* is freezing for suspend */
> @@ -97,7 +97,7 @@ register struct thread_info *__current_thread_info __asm__("$8");
> #define _TIF_ALLWORK_MASK (_TIF_WORK_MASK \
> | _TIF_SYSCALL_TRACE)
>
> -#define ALPHA_UAC_SHIFT 10
> +#define ALPHA_UAC_SHIFT TIF_UAC_NOPRINT
> #define ALPHA_UAC_MASK (1 << TIF_UAC_NOPRINT | 1 << TIF_UAC_NOFIX | \
> 1 << TIF_UAC_SIGBUS)
>
> diff --git a/arch/alpha/kernel/osf_sys.c b/arch/alpha/kernel/osf_sys.c
> index 326f0a2..2032f67 100644
> --- a/arch/alpha/kernel/osf_sys.c
> +++ b/arch/alpha/kernel/osf_sys.c
> @@ -42,6 +42,7 @@
> #include <asm/uaccess.h>
> #include <asm/system.h>
> #include <asm/sysinfo.h>
> +#include <asm/thread_info.h>
> #include <asm/hwrpb.h>
> #include <asm/processor.h>
>
> @@ -633,7 +634,7 @@ SYSCALL_DEFINE5(osf_getsysinfo, unsigned long, op, void __user *, buffer,
> case GSI_UACPROC:
> if (nbytes < sizeof(unsigned int))
> return -EINVAL;
> - w = (current_thread_info()->flags >> UAC_SHIFT) & UAC_BITMASK;
> + w = (current_thread_info()->flags >> ALPHA_UAC_SHIFT) & UAC_BITMASK;
> if (put_user(w, (unsigned int __user *)buffer))
> return -EFAULT;
> return 1;
> @@ -756,8 +757,8 @@ SYSCALL_DEFINE5(osf_setsysinfo, unsigned long, op, void __user *, buffer,
> case SSIN_UACPROC:
> again:
> old = current_thread_info()->flags;
> - new = old & ~(UAC_BITMASK << UAC_SHIFT);
> - new = new | (w & UAC_BITMASK) << UAC_SHIFT;
> + new = old & ~(UAC_BITMASK << ALPHA_UAC_SHIFT);
> + new = new | (w & UAC_BITMASK) << ALPHA_UAC_SHIFT;
> if (cmpxchg(¤t_thread_info()->flags,
> old, new) != old)
> goto again;
> --
> 1.7.3.4
Thanks for finding and fixing this bug. I've added it to my tree.
Matt
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