powerpc, hw_breakpoint: Fix off-by-one in checking access address

The code would accept an access to an address one byte past the end
of the requested range as legitimate, due to having a "<=" rather than
a "<".  This fixes that and cleans up the code a bit.

Signed-off-by: Paul Mackerras <paulus@samba.org>

diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
index ed39805..241e097 100644 (file)
--- a/arch/powerpc/kernel/hw_breakpoint.c
+++ b/arch/powerpc/kernel/hw_breakpoint.c
@@ -197,7 +197,6 @@ void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs)
  */
 int __kprobes hw_breakpoint_handler(struct die_args *args)
 {
-       bool is_ptrace_bp = false;
        int rc = NOTIFY_STOP;
        struct perf_event *bp;
        struct pt_regs *regs = args->regs;
@@ -208,6 +207,7 @@ int __kprobes hw_breakpoint_handler(struct die_args *args)
 
        /* Disable breakpoints during exception handling */
        set_dabr(0);
+
        /*
         * The counter may be concurrently released but that can only
         * occur from a call_rcu() path. We can then safely fetch
@@ -220,8 +220,6 @@ int __kprobes hw_breakpoint_handler(struct die_args *args)
        if (!bp)
                goto out;
        info = counter_arch_bp(bp);
-       is_ptrace_bp = (bp->overflow_handler == ptrace_triggered) ?
-                       true : false;
 
        /*
         * Return early after invoking user-callback function without restoring
@@ -229,7 +227,7 @@ int __kprobes hw_breakpoint_handler(struct die_args *args)
         * one-shot mode. The ptrace-ed process will receive the SIGTRAP signal
         * generated in do_dabr().
         */
-       if (is_ptrace_bp) {
+       if (bp->overflow_handler == ptrace_triggered) {
                perf_bp_event(bp, regs);
                rc = NOTIFY_DONE;
                goto out;
@@ -237,19 +235,12 @@ int __kprobes hw_breakpoint_handler(struct die_args *args)
 
        /*
         * Verify if dar lies within the address range occupied by the symbol
-        * being watched to filter extraneous exceptions.
+        * being watched to filter extraneous exceptions.  If it doesn't,
+        * we still need to single-step the instruction, but we don't
+        * generate an event.
         */
-       if (!((bp->attr.bp_addr <= dar) &&
-            (dar <= (bp->attr.bp_addr + bp->attr.bp_len)))) {
-               /*
-                * This exception is triggered not because of a memory access
-                * on the monitored variable but in the double-word address
-                * range in which it is contained. We will consume this
-                * exception, considering it as 'noise'.
-                */
-               info->extraneous_interrupt = true;
-       } else
-               info->extraneous_interrupt = false;
+       info->extraneous_interrupt = !((bp->attr.bp_addr <= dar) &&
+                       (dar - bp->attr.bp_addr < bp->attr.bp_len));
 
        /* Do not emulate user-space instructions, instead single-step them */
        if (user_mode(regs)) {