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Date: Wed, 10 Jan 2018 18:02:34 -0800
From: Kees Cook <keescook@...omium.org>
To: linux-kernel@...r.kernel.org
Cc: Kees Cook <keescook@...omium.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Windsor <dave@...lcore.net>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Christoph Lameter <cl@...ux.com>,
	"David S. Miller" <davem@...emloft.net>,
	Laura Abbott <labbott@...hat.com>,
	Mark Rutland <mark.rutland@....com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	Dave Kleikamp <dave.kleikamp@...cle.com>,
	Jan Kara <jack@...e.cz>,
	Luis de Bethencourt <luisbg@...nel.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Rik van Riel <riel@...hat.com>,
	Matthew Garrett <mjg59@...gle.com>,
	linux-fsdevel@...r.kernel.org,
	linux-arch@...r.kernel.org,
	netdev@...r.kernel.org,
	linux-mm@...ck.org,
	kernel-hardening@...ts.openwall.com
Subject: [PATCH 02/38] usercopy: Enhance and rename report_usercopy()

In preparation for refactoring the usercopy checks to pass offset to
the hardened usercopy report, this renames report_usercopy() to the
more accurate usercopy_abort(), marks it as noreturn because it is,
adds a hopefully helpful comment for anyone investigating such reports,
makes the function available to the slab allocators, and adds new "detail"
and "offset" arguments.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 mm/slab.h             |  6 ++++++
 mm/usercopy.c         | 24 +++++++++++++++++++-----
 tools/objtool/check.c |  1 +
 3 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/mm/slab.h b/mm/slab.h
index ad657ffa44e5..7d29e69ac310 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -526,4 +526,10 @@ static inline int cache_random_seq_create(struct kmem_cache *cachep,
 static inline void cache_random_seq_destroy(struct kmem_cache *cachep) { }
 #endif /* CONFIG_SLAB_FREELIST_RANDOM */
 
+#ifdef CONFIG_HARDENED_USERCOPY
+void __noreturn usercopy_abort(const char *name, const char *detail,
+			       bool to_user, unsigned long offset,
+			       unsigned long len);
+#endif
+
 #endif /* MM_SLAB_H */
diff --git a/mm/usercopy.c b/mm/usercopy.c
index 5df1e68d4585..8006baa4caac 100644
--- a/mm/usercopy.c
+++ b/mm/usercopy.c
@@ -58,11 +58,25 @@ static noinline int check_stack_object(const void *obj, unsigned long len)
 	return GOOD_STACK;
 }
 
-static void report_usercopy(unsigned long len, bool to_user, const char *type)
+/*
+ * If this function is reached, then CONFIG_HARDENED_USERCOPY has found an
+ * unexpected state during a copy_from_user() or copy_to_user() call.
+ * There are several checks being performed on the buffer by the
+ * __check_object_size() function. Normal stack buffer usage should never
+ * trip the checks, and kernel text addressing will always trip the check.
+ * For cache objects, copies must be within the object size.
+ */
+void __noreturn usercopy_abort(const char *name, const char *detail,
+			       bool to_user, unsigned long offset,
+			       unsigned long len)
 {
-	pr_emerg("kernel memory %s attempt detected %s '%s' (%lu bytes)\n",
-		to_user ? "exposure" : "overwrite",
-		to_user ? "from" : "to", type ? : "unknown", len);
+	pr_emerg("Kernel memory %s attempt detected %s %s%s%s%s (offset %lu, size %lu)!\n",
+		 to_user ? "exposure" : "overwrite",
+		 to_user ? "from" : "to",
+		 name ? : "unknown?!",
+		 detail ? " '" : "", detail ? : "", detail ? "'" : "",
+		 offset, len);
+
 	/*
 	 * For greater effect, it would be nice to do do_group_exit(),
 	 * but BUG() actually hooks all the lock-breaking and per-arch
@@ -260,6 +274,6 @@ void __check_object_size(const void *ptr, unsigned long n, bool to_user)
 		return;
 
 report:
-	report_usercopy(n, to_user, err);
+	usercopy_abort(err, NULL, to_user, 0, n);
 }
 EXPORT_SYMBOL(__check_object_size);
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 9b341584eb1b..ae39444896d4 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -138,6 +138,7 @@ static int __dead_end_function(struct objtool_file *file, struct symbol *func,
 		"__reiserfs_panic",
 		"lbug_with_loc",
 		"fortify_panic",
+		"usercopy_abort",
 	};
 
 	if (func->bind == STB_WEAK)
-- 
2.7.4

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