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authorJann Horn <jannh@google.com>2020-09-29 00:49:16 +0200
committerJosh Poimboeuf <jpoimboe@redhat.com>2020-10-02 09:28:08 -0500
commitb0b8e56b82c06b3bb6e5fb66d0e9c9c3fd3ce555 (patch)
treeec44f42a4be37fcafde25ca48bac9fda8dda1045 /tools/objtool
parent14db1f0a93331d0958e90da522c429ff0890d2d6 (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(&copy_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.c2
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",