The following commit has been merged into the objtool/core branch of tip:
Commit-ID: b0b8e56b82c06b3bb6e5fb66d0e9c9c3fd3ce555
Gitweb: https://git.kernel.org/tip/b0b8e56b82c06b3bb6e5fb66d0e9c9c3fd3ce555
Author: Jann Horn <jannh@xxxxxxxxxx>
AuthorDate: Tue, 29 Sep 2020 00:49:16 +02:00
Committer: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
CommitterDate: Fri, 02 Oct 2020 09:28:08 -05:00
objtool: Permit __kasan_check_{read,write} under UACCESS
Building linux-next with JUMP_LABEL=n and KASAN=y, I got this objtool
warning:
arch/x86/lib/copy_mc.o: warning: objtool: copy_mc_to_user()+0x22: call to
__kasan_check_read() with UACCESS enabled
What happens here is that copy_mc_to_user() branches on a static key in a
UACCESS region:
__uaccess_begin();
if (static_branch_unlikely(©_mc_fragile_key))
ret = copy_mc_fragile(to, from, len);
ret = copy_mc_generic(to, from, len);
__uaccess_end();
and the !CONFIG_JUMP_LABEL version of static_branch_unlikely() uses
static_key_enabled(), which uses static_key_count(), which uses
atomic_read(), which calls instrument_atomic_read(), which uses
kasan_check_read(), which is __kasan_check_read().
Let's permit these KASAN helpers in UACCESS regions - static keys should
probably work under UACCESS, I think.
PeterZ adds:
It's not a matter of permitting, it's a matter of being safe and
correct. In this case it is, because it's a thin wrapper around
check_memory_region() which was already marked safe.
check_memory_region() is correct because the only thing it ends up
calling is kasa_report() and that is also marked safe because that is
annotated with user_access_save/restore() before it does anything else.
On top of that, all of KASAN is noinstr, so nothing in here will end up
in tracing and/or call schedule() before the user_access_save().
Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
tools/objtool/check.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 2df9f76..3d14134 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -583,6 +583,8 @@ static const char *uaccess_safe_builtin[] = {
"__asan_store4_noabort",
"__asan_store8_noabort",
"__asan_store16_noabort",
+ "__kasan_check_read",
+ "__kasan_check_write",
/* KASAN in-line */
"__asan_report_load_n_noabort",
"__asan_report_load1_noabort",
|