[tip:perf/core] perf/x86/hw_breakpoints: Fix check for kernel-space breakpoints

[tip-bot for Andy Lutomirski <tipbot@zytor.com>]

Commit-ID:  27747f8bc355a2808ca9e490ab6866acd85b4c16
Gitweb:     http://git.kernel.org/tip/27747f8bc355a2808ca9e490ab6866acd85b4c16
Author:     Andy Lutomirski <luto@kernel.org>
AuthorDate: Thu, 30 Jul 2015 20:32:42 -0700
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 4 Aug 2015 10:16:55 +0200

perf/x86/hw_breakpoints: Fix check for kernel-space breakpoints

The check looked wrong, although I think it was actually safe.  TASK_SIZE
is unnecessarily small for compat tasks, and it wasn't possible to make
a range breakpoint so large it started in user space and ended in kernel
space.

Nonetheless, let's fix up the check for the benefit of future
readers.  A breakpoint is in the kernel if either end is in the
kernel.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/136be387950e78f18cea60e9d1bef74465d0ee8f.1438312874.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/hw_breakpoint.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
index 6f345d3..50a3fad 100644
--- a/arch/x86/kernel/hw_breakpoint.c
+++ b/arch/x86/kernel/hw_breakpoint.c
@@ -180,7 +180,11 @@ int arch_check_bp_in_kernelspace(struct perf_event *bp)
 	va = info->address;
 	len = bp->attr.bp_len;
 
-	return (va >= TASK_SIZE) && ((va + len - 1) >= TASK_SIZE);
+	/*
+	 * We don't need to worry about va + len - 1 overflowing:
+	 * we already require that va is aligned to a multiple of len.
+	 */
+	return (va >= TASK_SIZE_MAX) || ((va + len - 1) >= TASK_SIZE_MAX);
 }
 
 int arch_bp_generic_fields(int x86_len, int x86_type,