linux-kernel - [PATCH 10/20] x86/uaccess,ubsan: Fix UBSAN vs SMAP

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Date:   Thu, 07 Mar 2019 12:45:21 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     torvalds@...ux-foundation.org, tglx@...utronix.de, hpa@...or.com,
        julien.thierry@....com, will.deacon@....com, luto@...capital.net,
        mingo@...nel.org, catalin.marinas@....com, james.morse@....com,
        valentin.schneider@....com, brgerst@...il.com, jpoimboe@...hat.com,
        luto@...nel.org, bp@...en8.de, dvlasenk@...hat.com
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        dvyukov@...gle.com, rostedt@...dmis.org
Subject: [PATCH 10/20] x86/uaccess,ubsan: Fix UBSAN vs SMAP

UBSAN can insert extra code in random locations; including AC=1
sections. Typically this code is not safe and needs wrapping.

So far, only __ubsan_handle_type_mismatch* have been observed in AC=1
sections and therefore only those are annotated.

Cc: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 lib/Makefile |    1 +
 lib/ubsan.c  |    4 ++++
 2 files changed, 5 insertions(+)

--- a/lib/Makefile
+++ b/lib/Makefile
@@ -263,6 +263,7 @@ obj-$(CONFIG_UCS2_STRING) += ucs2_string
 obj-$(CONFIG_UBSAN) += ubsan.o
 
 UBSAN_SANITIZE_ubsan.o := n
+CFLAGS_ubsan.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
 
 obj-$(CONFIG_SBITMAP) += sbitmap.o
 
--- a/lib/ubsan.c
+++ b/lib/ubsan.c
@@ -17,6 +17,7 @@
 #include <linux/kernel.h>
 #include <linux/types.h>
 #include <linux/sched.h>
+#include <linux/uaccess.h>
 
 #include "ubsan.h"
 
@@ -313,6 +314,7 @@ static void handle_object_size_mismatch(
 static void ubsan_type_mismatch_common(struct type_mismatch_data_common *data,
 				unsigned long ptr)
 {
+	unsigned long flags = user_access_save();
 
 	if (!ptr)
 		handle_null_ptr_deref(data);
@@ -320,6 +322,8 @@ static void ubsan_type_mismatch_common(s
 		handle_misaligned_access(data, ptr);
 	else
 		handle_object_size_mismatch(data, ptr);
+
+	user_access_restore(flags);
 }
 
 void __ubsan_handle_type_mismatch(struct type_mismatch_data *data,