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authorFrederic Weisbecker <fweisbec@gmail.com>2010-04-18 20:11:53 +0400
committerFrederic Weisbecker <fweisbec@gmail.com>2010-05-01 06:32:10 +0400
commitb2812d031dea86926e9c10f7714af33ac2f6b43d (patch)
treea48b18b49fa064e89b7b03e057e46e5a294a8053 /kernel/hw_breakpoint.c
parent87e9b2024659c614a876ce359a57e98a47b5ef37 (diff)
downloadlinux-b2812d031dea86926e9c10f7714af33ac2f6b43d.tar.xz
hw-breakpoints: Change/Enforce some breakpoints policies
The current policies of breakpoints in x86 and SH are the following: - task bound breakpoints can only break on userspace addresses - cpu wide breakpoints can only break on kernel addresses The former rule prevents ptrace breakpoints to be set to trigger on kernel addresses, which is good. But as a side effect, we can't breakpoint on kernel addresses for task bound breakpoints. The latter rule simply makes no sense, there is no reason why we can't set breakpoints on userspace while performing cpu bound profiles. We want the following new policies: - task bound breakpoint can set userspace address breakpoints, with no particular privilege required. - task bound breakpoints can set kernelspace address breakpoints but must be privileged to do that. - cpu bound breakpoints can do what they want as they are privileged already. To implement these new policies, this patch checks if we are dealing with a kernel address breakpoint, if so and if the exclude_kernel parameter is set, we tell the user that the breakpoint is invalid, which makes a good generic ptrace protection. If we don't have exclude_kernel, ensure the user has the right privileges as kernel breakpoints are quite sensitive (risk of trap recursion attacks and global performance impacts). [ Paul Mundt: keep addr space check for sh signal delivery and fix double function declaration] Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com> Cc: K. Prasad <prasad@linux.vnet.ibm.com> Cc: Paul Mundt <lethal@linux-sh.org> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Jason Wessel <jason.wessel@windriver.com> Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Diffstat (limited to 'kernel/hw_breakpoint.c')
-rw-r--r--kernel/hw_breakpoint.c26
1 files changed, 24 insertions, 2 deletions
diff --git a/kernel/hw_breakpoint.c b/kernel/hw_breakpoint.c
index 9ed9ae3a48b3..89e8a050c43a 100644
--- a/kernel/hw_breakpoint.c
+++ b/kernel/hw_breakpoint.c
@@ -308,6 +308,28 @@ int dbg_release_bp_slot(struct perf_event *bp)
return 0;
}
+static int validate_hw_breakpoint(struct perf_event *bp)
+{
+ int ret;
+
+ ret = arch_validate_hwbkpt_settings(bp);
+ if (ret)
+ return ret;
+
+ if (arch_check_bp_in_kernelspace(bp)) {
+ if (bp->attr.exclude_kernel)
+ return -EINVAL;
+ /*
+ * Don't let unprivileged users set a breakpoint in the trap
+ * path to avoid trap recursion attacks.
+ */
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+ }
+
+ return 0;
+}
+
int register_perf_hw_breakpoint(struct perf_event *bp)
{
int ret;
@@ -316,7 +338,7 @@ int register_perf_hw_breakpoint(struct perf_event *bp)
if (ret)
return ret;
- ret = arch_validate_hwbkpt_settings(bp, bp->ctx->task);
+ ret = validate_hw_breakpoint(bp);
/* if arch_validate_hwbkpt_settings() fails then release bp slot */
if (ret)
@@ -363,7 +385,7 @@ int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *att
if (attr->disabled)
goto end;
- err = arch_validate_hwbkpt_settings(bp, bp->ctx->task);
+ err = validate_hw_breakpoint(bp);
if (!err)
perf_event_enable(bp);