linux-kernel - Re: [PATCH v3 22/22] x86/int3: Ensure that poke_int3

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Message-ID: <20200219172014.GI14946@hirez.programming.kicks-ass.net>
Date:   Wed, 19 Feb 2020 18:20:14 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Andy Lutomirski <luto@...nel.org>, tony.luck@...el.com,
        Frederic Weisbecker <frederic@...nel.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: [PATCH v3 22/22] x86/int3: Ensure that poke_int3_handler() is
 not sanitized

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);