Re: [PATCH v3 22/22] x86/int3: Ensure that poke_int3_handler() is not sanitized

Peter Zijlstra
2020-02-19T17:20:42Z

On Wed, Feb 19, 2020 at 05:30:25PM +0100, Peter Zijlstra wrote:

> By inlining everything in poke_int3_handler() (except bsearch :/) we can
> mark the whole function off limits to everything and call it a day. That
> simplicity has been the guiding principle so far.
>
> Alternatively we can provide an __always_inline variant of bsearch().

This reduces the __no_sanitize usage to just the exception entry
(do_int3) and the critical function: poke_int3_handler().

Is this more acceptible?

--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -979,7 +979,7 @@ static __always_inline void *text_poke_a
return _stext + tp->rel_addr;
}

-static int notrace __no_sanitize patch_cmp(const void *key, const void *elt)
+static __always_inline int patch_cmp(const void *key, const void *elt)
{
struct text_poke_loc *tp = (struct text_poke_loc *) elt;

@@ -989,7 +989,6 @@ static int notrace __no_sanitize patch_c
return 1;
return 0;
}
-NOKPROBE_SYMBOL(patch_cmp);

int notrace __no_sanitize poke_int3_handler(struct pt_regs *regs)
{
@@ -1024,9 +1023,9 @@ int notrace __no_sanitize poke_int3_hand
* Skip the binary search if there is a single member in the vector.
*/
if (unlikely(desc->nr_entries > 1)) {
- tp = bsearch(ip, desc->vec, desc->nr_entries,
- sizeof(struct text_poke_loc),
- patch_cmp);
+ tp = __bsearch(ip, desc->vec, desc->nr_entries,
+ sizeof(struct text_poke_loc),
+ patch_cmp);
if (!tp)
goto out_put;
} else {
--- a/include/linux/bsearch.h
+++ b/include/linux/bsearch.h
@@ -4,7 +4,29 @@

#include <linux/types.h>

-void *bsearch(const void *key, const void *base, size_t num, size_t size,
- cmp_func_t cmp);
+static __always_inline
+void *__bsearch(const void *key, const void *base, size_t num, size_t size, cmp_func_t cmp)
+{
+ const char *pivot;
+ int result;
+
+ while (num > 0) {
+ pivot = base + (num >> 1) * size;
+ result = cmp(key, pivot);
+
+ if (result == 0)
+ return (void *)pivot;
+
+ if (result > 0) {
+ base = pivot + size;
+ num--;
+ }
+ num >>= 1;
+ }
+
+ return NULL;
+}
+
+extern void *bsearch(const void *key, const void *base, size_t num, size_t size, cmp_func_t cmp);

#endif /* _LINUX_BSEARCH_H */
--- a/lib/bsearch.c
+++ b/lib/bsearch.c
@@ -28,27 +28,9 @@
* the key and elements in the array are of the same type, you can use
* the same comparison function for both sort() and bsearch().
*/
-void __no_sanitize *bsearch(const void *key, const void *base, size_t num, size_t size,
- cmp_func_t cmp)
+void *bsearch(const void *key, const void *base, size_t num, size_t size, cmp_func_t cmp)
{
- const char *pivot;
- int result;
-
- while (num > 0) {
- pivot = base + (num >> 1) * size;
- result = cmp(key, pivot);
-
- if (result == 0)
- return (void *)pivot;
-
- if (result > 0) {
- base = pivot + size;
- num--;
- }
- num >>= 1;
- }
-
- return NULL;
+ __bsearch(key, base, num, size, cmp);
}
EXPORT_SYMBOL(bsearch);
NOKPROBE_SYMBOL(bsearch);