ptrace/x86: revert "hw_breakpoints: Fix racy access to ptrace breakpoints"

This reverts commit 87dc669ba257 ("hw_breakpoints: Fix racy access to
ptrace breakpoints").

The patch was fine but we can no longer race with SIGKILL after commit
9899d11f6544 ("ptrace: ensure arch_ptrace/ptrace_request can never race
with SIGKILL"), the __TASK_TRACED tracee can't be woken up and
->ptrace_bps[] can't go away.

The patch only removes ptrace_get_breakpoints/ptrace_put_breakpoints and
does a couple of "while at it" cleanups, it doesn't remove other changes
from the reverted commit.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Jan Kratochvil <jan.kratochvil@redhat.com>
Cc: Michael Neuling <mikey@neuling.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Prasad <prasad@linux.vnet.ibm.com>
Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 23 deletions

diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 29a8120e6fe8..7a98b21945aa 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -641,9 +641,6 @@ static int ptrace_write_dr7(struct task_struct *tsk, unsigned long data)
         unsigned len, type;
         struct perf_event *bp;
 
-        if (ptrace_get_breakpoints(tsk) < 0)
-                return -ESRCH;
-
         data &= ~DR_CONTROL_RESERVED;
         old_dr7 = ptrace_get_dr7(thread->ptrace_bps);
 restore:
@@ -692,9 +689,7 @@ restore:
                 goto restore;
         }
 
-        ptrace_put_breakpoints(tsk);
-
-        return ((orig_ret < 0) ? orig_ret : rc);
+        return orig_ret < 0 ? orig_ret : rc;
 }
 
 /*
@@ -706,18 +701,10 @@ static unsigned long ptrace_get_debugreg(struct task_struct *tsk, int n)
         unsigned long val = 0;
 
         if (n < HBP_NUM) {
-                struct perf_event *bp;
+                struct perf_event *bp = thread->ptrace_bps[n];
 
-                if (ptrace_get_breakpoints(tsk) < 0)
-                        return -ESRCH;
-
-                bp = thread->ptrace_bps[n];
-                if (!bp)
-                        val = 0;
-                else
+                if (bp)
                         val = bp->hw.info.address;
-
-                ptrace_put_breakpoints(tsk);
         } else if (n == 6) {
                 val = thread->debugreg6;
          } else if (n == 7) {
@@ -734,9 +721,6 @@ static int ptrace_set_breakpoint_addr(struct task_struct *tsk, int nr,
         struct perf_event_attr attr;
         int err = 0;
 
-        if (ptrace_get_breakpoints(tsk) < 0)
-                return -ESRCH;
-
         if (!t->ptrace_bps[nr]) {
                 ptrace_breakpoint_init(&attr);
                 /*
@@ -762,7 +746,7 @@ static int ptrace_set_breakpoint_addr(struct task_struct *tsk, int nr,
                  */
                 if (IS_ERR(bp)) {
                         err = PTR_ERR(bp);
-                        goto put;
+                        goto out;
                 }
 
                 t->ptrace_bps[nr] = bp;
@@ -773,9 +757,7 @@ static int ptrace_set_breakpoint_addr(struct task_struct *tsk, int nr,
                 attr.bp_addr = addr;
                 err = modify_user_hw_breakpoint(bp, &attr);
         }
-
-put:
-        ptrace_put_breakpoints(tsk);
+out:
         return err;
 }