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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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.