On Fri, 2007-09-07 at 09:11 -0600, David Mosberger-Tang wrote: > Anything that avoids complicating the kernel exit path is worth doing! > The exit path is complicated enough as it is. > > --david > > On 9/7/07, Petr Tesarik <ptesarik@xxxxxxx> wrote: > > -----BEGIN PGP SIGNED MESSAGE----- > > Hash: SHA1 > > > > Shaohua Li wrote: > > > On Thu, 2007-09-06 at 15:59 +0200, Petr Tesarik wrote: > > >>[...] > > >> So, what happens if upon syscall entry notification the debugger > > >> modifies the part of the RBS (in user-space) which corresponds to the > > >> arguments of that syscall? Currently, the syscall takes the modified > > >> arguments, but with your change it would still take the stale data > > >> from > > >> the kernel RBS. > > > The patch does sync from user RBS to kernel RBS just after syscall trace > > > enter. this is an exception I said doing sync just before syscall > > > return. I thought this covers your case, no? > > > > Ah, I'm sorry, I missed that part of the patch. Well, if we have to do a > > sync on every syscall_trace_enter() and syscall_trace_leave(), then the > > only cases where introducing TIF_RESTORE_RSE saves us a duplicate sync > > seems to be in the clone/fork and exit paths. In other words, it's > > probably not worth the added complexity. But since you have written the > > whole complex thing already, I have no objections against it. Ok, this is a simplified patch. please review. Signed-off-by: Shaohua Li <shaohua.li@xxxxxxxxx> --- arch/ia64/kernel/ptrace.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++ include/asm-ia64/ptrace.h | 2 + include/linux/ptrace.h | 4 ++ kernel/signal.c | 5 ++- 4 files changed, 72 insertions(+), 1 deletion(-) Index: linux/arch/ia64/kernel/ptrace.c =================================================================== --- linux.orig/arch/ia64/kernel/ptrace.c 2007-09-06 13:06:49.000000000 +0800 +++ linux/arch/ia64/kernel/ptrace.c 2007-09-11 11:33:35.000000000 +0800 @@ -547,6 +547,62 @@ ia64_sync_user_rbs (struct task_struct * return 0; } +static long +ia64_sync_kernel_rbs (struct task_struct *child, struct switch_stack *sw, + unsigned long user_rbs_start, unsigned long user_rbs_end) +{ + unsigned long addr, val; + long ret; + + /* now copy word for word from user rbs to kernel rbs: */ + for (addr = user_rbs_start; addr < user_rbs_end; addr += 8) { + if (access_process_vm(child, addr, &val, sizeof(val), 0) + != sizeof(val)) + return -EIO; + + ret = ia64_poke(child, sw, user_rbs_end, addr, val); + if (ret < 0) + return ret; + } + return 0; +} + +#define RBS_SYNC_TO_USER 0 +#define RBS_SYNC_TO_KERNEL 1 +static void do_sync_rbs(struct unw_frame_info *info, void *arg) +{ + struct pt_regs *pt; + unsigned long urbs_end; + int to_user = (unsigned long)arg; + + if (unw_unwind_to_user(info) < 0) + return; + pt = task_pt_regs(info->task); + urbs_end = ia64_get_user_rbs_end(info->task, pt, NULL); + + if (to_user == RBS_SYNC_TO_USER) + ia64_sync_user_rbs(info->task, info->sw, pt->ar_bspstore, urbs_end); + else + ia64_sync_kernel_rbs(info->task, info->sw, pt->ar_bspstore, urbs_end); +} + +/* + * when a thread is stopped (ptraced), debugger might change thread's user + * stack (change memory directly), and we must avoid the RSE stored in kernel + * to override user stack (user space's RSE is newer than kernel's in the + * case). To workaround the issue, we copy kernel RSE to user RSE before the + * task is stopped, so user RSE has updated data. we then copy user RSE to + * kernel after the task is resummed from traced stop and kernel will use the + * newer RSE to return to user. + */ +void arch_ptrace_stop(int before_suspend) +{ + if (before_suspend) + unw_init_running(do_sync_rbs, (void *)RBS_SYNC_TO_USER); + else + unw_init_running(do_sync_rbs, (void *)RBS_SYNC_TO_KERNEL); +} + static inline int thread_matches (struct task_struct *thread, unsigned long addr) { @@ -1422,6 +1478,7 @@ sys_ptrace (long request, pid_t pid, uns struct task_struct *child; struct switch_stack *sw; long ret; + struct unw_frame_info info; lock_kernel(); ret = -EPERM; @@ -1481,6 +1538,11 @@ sys_ptrace (long request, pid_t pid, uns /* write the word at location addr */ urbs_end = ia64_get_user_rbs_end(child, pt, NULL); ret = ia64_poke(child, sw, urbs_end, addr, data); + + /* Make sure user RBS has the latest data */ + unw_init_from_blocked_task(&info, child); + do_sync_rbs(&info, RBS_SYNC_TO_USER); + goto out_tsk; case PTRACE_PEEKUSR: Index: linux/include/asm-ia64/ptrace.h =================================================================== --- linux.orig/include/asm-ia64/ptrace.h 2007-08-29 11:26:33.000000000 +0800 +++ linux/include/asm-ia64/ptrace.h 2007-09-11 09:53:04.000000000 +0800 @@ -303,6 +303,8 @@ struct switch_stack { extern void ia64_increment_ip (struct pt_regs *pt); extern void ia64_decrement_ip (struct pt_regs *pt); + extern void arch_ptrace_stop(int); + #define HAVE_ARCH_PTRACE_STOP #endif /* !__KERNEL__ */ /* pt_all_user_regs is used for PTRACE_GETREGS PTRACE_SETREGS */ Index: linux/kernel/signal.c =================================================================== --- linux.orig/kernel/signal.c 2007-09-11 09:33:14.000000000 +0800 +++ linux/kernel/signal.c 2007-09-11 10:55:05.000000000 +0800 @@ -1599,15 +1599,18 @@ static void ptrace_stop(int exit_code, i current->last_siginfo = info; current->exit_code = exit_code; + spin_unlock_irq(¤t->sighand->siglock); + arch_ptrace_stop(1); /* Let the debugger run. */ set_current_state(TASK_TRACED); - spin_unlock_irq(¤t->sighand->siglock); + try_to_freeze(); read_lock(&tasklist_lock); if (may_ptrace_stop()) { do_notify_parent_cldstop(current, CLD_TRAPPED); read_unlock(&tasklist_lock); schedule(); + arch_ptrace_stop(0); } else { /* * By the time we got the lock, our tracer went away. Index: linux/include/linux/ptrace.h =================================================================== --- linux.orig/include/linux/ptrace.h 2007-08-29 11:26:33.000000000 +0800 +++ linux/include/linux/ptrace.h 2007-09-11 09:52:32.000000000 +0800 @@ -128,6 +128,10 @@ int generic_ptrace_pokedata(struct task_ #define force_successful_syscall_return() do { } while (0) #endif +#ifndef HAVE_ARCH_PTRACE_STOP +#define arch_ptrace_stop(a) do { } while (0) +#endif + #endif #endif - To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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