[PATCH 09/19] x86, mpx: trace entry to bounds exception paths

Dave Hansen
2015-05-27T18:40:16Z

From: Dave Hansen <dave.hansen@linux.intel.com>

There are two basic things that can happen as the result of
a bounds exception (#BR):

1. We allocate a new bounds table
2. We pass up a bounds exception to userspace.

This patch adds a trace point for the case where we are
passing the exception up to userspace with a signal.

We are also explicit that we're printing out the inverse of
the 'upper' that we encounter. If you want to filter, for
instance, you need to ~ the value first. The reason we do
this is because of how 'upper' is stored in the bounds table.
If a pointer's range is:

0x1000 -> 0x2000

it is stored in the bounds table as (32-bits here for brevity):

lower: 0x00001000
upper: 0xffffdfff

That is so that an all 0's entry:

lower: 0x00000000
upper: 0x00000000

corresponds to the "init" bounds which store a *range* of:

0x00000000 -> 0xffffffff

That is, by far, the common case, and that lets us use the
zero page, or deduplicate the memory, etc... The 'upper'
stored in the table is gibberish to print by itself, so we
print ~upper to get the *actual*, logical, human-readable
value printed out.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
---

b/arch/x86/include/asm/trace/mpx.h | 34 ++++++++++++++++++++++++++++++++++
b/arch/x86/mm/mpx.c | 1 +
2 files changed, 35 insertions(+)

diff -puN arch/x86/include/asm/trace/mpx.h~x86-mpx-trace-1 arch/x86/include/asm/trace/mpx.h
--- a/arch/x86/include/asm/trace/mpx.h~x86-mpx-trace-1 2015-05-27 09:32:17.938598834 -0700
+++ b/arch/x86/include/asm/trace/mpx.h 2015-05-27 09:32:17.943599059 -0700
@@ -8,6 +8,40 @@

#ifdef CONFIG_X86_INTEL_MPX

+TRACE_EVENT(mpx_bounds_register_exception,
+
+ TP_PROTO(void *addr_referenced,
+ struct bndreg *bndreg),
+ TP_ARGS(addr_referenced, bndreg),
+
+ TP_STRUCT__entry(
+ __field(void *, addr_referenced)
+ __field(u64, lower_bound)
+ __field(u64, upper_bound)
+ ),
+
+ TP_fast_assign(
+ __entry->addr_referenced = addr_referenced;
+ __entry->lower_bound = bndreg->lower_bound;
+ __entry->upper_bound = bndreg->upper_bound;
+ ),
+ /*
+ * Note that we are printing out the '~' of the upper
+ * bounds register here. It is actually stored in its
+ * one's complement form so that its 'init' state
+ * corresponds to all 0's. But, that looks like
+ * gibberish when printed out, so print out the 1's
+ * complement instead of the actual value here. Note
+ * though that you still need to specify filters for the
+ * actual value, not the displayed one.
+ */
+ TP_printk("address referenced: 0x%p bounds: lower: 0x%llx ~upper: 0x%llx",
+ __entry->addr_referenced,
+ __entry->lower_bound,
+ ~__entry->upper_bound
+ )
+);
+
TRACE_EVENT(bounds_exception_mpx,

TP_PROTO(struct bndcsr *bndcsr),
diff -puN arch/x86/mm/mpx.c~x86-mpx-trace-1 arch/x86/mm/mpx.c
--- a/arch/x86/mm/mpx.c~x86-mpx-trace-1 2015-05-27 09:32:17.940598924 -0700
+++ b/arch/x86/mm/mpx.c 2015-05-27 09:32:17.944599105 -0700
@@ -335,6 +335,7 @@ siginfo_t *mpx_generate_siginfo(struct p
err = -EINVAL;
goto err_out;
}
+ trace_mpx_bounds_register_exception(info->si_addr, bndreg);
return info;
err_out:
/* info might be NULL, but kfree() handles that */
_