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| author | Jann Horn <jannh@google.com> | 2020-09-29 00:49:16 +0200 |
|---|---|---|
| committer | Josh Poimboeuf <jpoimboe@redhat.com> | 2020-10-02 09:28:08 -0500 |
| commit | b0b8e56b82c06b3bb6e5fb66d0e9c9c3fd3ce555 (patch) | |
| tree | ec44f42a4be37fcafde25ca48bac9fda8dda1045 /tools/objtool | |
| parent | 14db1f0a93331d0958e90da522c429ff0890d2d6 (diff) | |
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@google.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Diffstat (limited to 'tools/objtool')
| -rw-r--r-- | tools/objtool/check.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 2df9f769412e..3d14134c4e97 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", |