Jann Horn b0b8e56b82 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>		2020-10-02 09:28:08 -05:00
..
arch/x86	objtool: Decode unwind hint register depending on architecture	2020-09-10 10:43:13 -05:00
Documentation	objtool: Add support for intra-function calls	2020-04-30 20:14:33 +02:00
.gitignore	.gitignore: add SPDX License Identifier	2020-03-25 11:50:48 +01:00
arch.h	objtool: Decode unwind hint register depending on architecture	2020-09-10 10:43:13 -05:00
Build	objtool: Enable compilation of objtool for all architectures	2020-05-20 09:17:28 -05:00
builtin-check.c	objtool: Move ORC logic out of check()	2020-09-01 17:19:11 -05:00
builtin-orc.c	objtool: Move ORC logic out of check()	2020-09-01 17:19:11 -05:00
builtin.h	objtool: Implement noinstr validation	2020-04-22 10:53:50 +02:00
cfi.h	objtool: Fix !CFI insn_state propagation	2020-04-22 10:53:50 +02:00
check.c	objtool: Permit __kasan_check_{read,write} under UACCESS	2020-10-02 09:28:08 -05:00
check.h	objtool: Refactor jump table code to support other architectures	2020-09-10 10:43:13 -05:00
elf.c	x86/static_call: Add inline static call implementation for x86-64	2020-09-01 09:58:05 +02:00
elf.h	x86/static_call: Add inline static call implementation for x86-64	2020-09-01 09:58:05 +02:00
Makefile	objtool: Define 'struct orc_entry' only when needed	2020-09-01 17:19:12 -05:00
objtool.c	objtool: Move object file loading out of check()	2020-09-01 17:19:07 -05:00
objtool.h	objtool: Abstract alternative special case handling	2020-09-10 10:43:13 -05:00
orc_dump.c	objtool: Make unwind hint definitions available to other architectures	2020-09-10 10:43:13 -05:00
orc_gen.c	objtool: Make unwind hint definitions available to other architectures	2020-09-10 10:43:13 -05:00
special.c	objtool: Abstract alternative special case handling	2020-09-10 10:43:13 -05:00
special.h	objtool: Refactor jump table code to support other architectures	2020-09-10 10:43:13 -05:00
sync-check.sh	objtool: Make unwind hint definitions available to other architectures	2020-09-10 10:43:13 -05:00
warn.h	objtool: Rename find_containing_func()	2020-03-25 18:28:29 +01:00
weak.c	objtool: Abstract alternative special case handling	2020-09-10 10:43:13 -05:00