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From: Jiri Olsa <jolsa@kernel.org>
To: Ingo Molnar <mingo@kernel.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: lkml <linux-kernel@vger.kernel.org>,
	Namhyung Kim <namhyung@kernel.org>,
	David Ahern <dsahern@gmail.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Milind Chabbi <chabbi.milind@gmail.com>,
	Oleg Nesterov <oleg@redhat.com>
Subject: [PATCH 2/5] perf/hw_breakpoint: Modify breakpoint even if the new attr has disabled set
Date: Mon, 27 Aug 2018 11:12:25 +0200
Message-ID: <20180827091228.2878-3-jolsa@kernel.org> (raw)
In-Reply-To: <20180827091228.2878-1-jolsa@kernel.org>

We need to change the breakpoint even if the attr with
new fields has disabled set to true.

Current code prevents following user code to change
the breakpoint address:

  ptrace(PTRACE_POKEUSER, child, offsetof(struct user, u_debugreg[0]), addr_1)
  ptrace(PTRACE_POKEUSER, child, offsetof(struct user, u_debugreg[0]), addr_2)
  ptrace(PTRACE_POKEUSER, child, offsetof(struct user, u_debugreg[7]), dr7)

The first PTRACE_POKEUSER creates the breakpoint with
attr.disabled set to true:

  ptrace_set_breakpoint_addr(nr = 0)
    struct perf_event *bp = t->ptrace_bps[nr];

    ptrace_register_breakpoint(..., disabled = true)
      ptrace_fill_bp_fields(..., disabled)
      register_user_hw_breakpoint

So the second PTRACE_POKEUSER will be omitted:

  ptrace_set_breakpoint_addr(nr = 0)
    struct perf_event *bp = t->ptrace_bps[nr];
    struct perf_event_attr attr = bp->attr;

    modify_user_hw_breakpoint(bp, &attr)
      if (!attr->disabled)
        modify_user_hw_breakpoint_check

Acked-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Reported-by: Milind Chabbi <chabbi.milind@gmail.com>
Link: http://lkml.kernel.org/n/tip-yjhgplc28gk5gfzt7ceooe6z@git.kernel.org
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 kernel/events/hw_breakpoint.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
index b3814fce5ecb..fb229d9c7f3c 100644
--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c
@@ -509,6 +509,8 @@ modify_user_hw_breakpoint_check(struct perf_event *bp, struct perf_event_attr *a
  */
 int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
 {
+	int err;
+
 	/*
 	 * modify_user_hw_breakpoint can be invoked with IRQs disabled and hence it
 	 * will not be possible to raise IPIs that invoke __perf_event_disable.
@@ -520,11 +522,11 @@ int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *att
 	else
 		perf_event_disable(bp);
 
-	if (!attr->disabled) {
-		int err = modify_user_hw_breakpoint_check(bp, attr, false);
+	err = modify_user_hw_breakpoint_check(bp, attr, false);
+	if (err)
+		return err;
 
-		if (err)
-			return err;
+	if (!attr->disabled) {
 		perf_event_enable(bp);
 		bp->attr.disabled = 0;
 	}
-- 
2.17.1


  parent reply index

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-27  9:12 [PATCHv4 0/5] perf/hw_breakpoint: Fix breakpoint modify Jiri Olsa
2018-08-27  9:12 ` [PATCH 1/5] perf tests: Add breakpoint modify tests Jiri Olsa
2018-09-06 13:01   ` [tip:perf/core] " tip-bot for Jiri Olsa
2018-08-27  9:12 ` Jiri Olsa [this message]
2018-09-06 13:02   ` [tip:perf/core] perf/hw_breakpoint: Modify breakpoint even if the new attr has disabled set tip-bot for Jiri Olsa
2018-08-27  9:12 ` [PATCH 3/5] perf/hw_breakpoint: Remove superfluous bp->attr.disabled = 0 Jiri Olsa
2018-09-06 13:02   ` [tip:perf/core] " tip-bot for Jiri Olsa
2018-08-27  9:12 ` [PATCH 4/5] perf/hw_breakpoint: Enable breakpoint in modify_user_hw_breakpoint Jiri Olsa
2018-09-06 13:03   ` [tip:perf/core] " tip-bot for Jiri Olsa
2018-08-27  9:12 ` [PATCH 5/5] perf/hw_breakpoint: Simplify breakpoint enable in perf_event_modify_breakpoint Jiri Olsa
2018-09-06 13:03   ` [tip:perf/core] " tip-bot for Jiri Olsa
2018-08-30 18:39 ` [PATCHv4 0/5] perf/hw_breakpoint: Fix breakpoint modify Arnaldo Carvalho de Melo
  -- strict thread matches above, loose matches on Subject: below --
2018-08-10 10:47 [PATCHv3 " Jiri Olsa
2018-08-10 10:47 ` [PATCH 2/5] perf/hw_breakpoint: Modify breakpoint even if the new attr has disabled set Jiri Olsa
2018-08-17 14:27   ` Frederic Weisbecker
2018-08-09 12:03 [PATCHv2 0/5] perf/hw_breakpoint: Fix breakpoint modify Jiri Olsa
2018-08-09 12:03 ` [PATCH 2/5] perf/hw_breakpoint: Modify breakpoint even if the new attr has disabled set Jiri Olsa

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