On Wed, May 17, 2017 at 03:21:41PM -0700, Eric Biggers wrote: > On Wed, May 17, 2017 at 03:44:27PM -0500, Josh Poimboeuf wrote: > > On Tue, May 16, 2017 at 09:03:08PM -0700, Eric Biggers wrote: > > > From: Eric Biggers <ebiggers@xxxxxxxxxx> > > > > > > When using the "aes-asm" implementation of AES (*not* the AES-NI > > > implementation) on an x86_64, v4.12-rc1 kernel with lockdep enabled, the > > > following warning was reported, along with a long unwinder dump: > > > > > > WARNING: kernel stack regs at ffffc90000643558 in kworker/u4:2:155 has bad 'bp' value 000000000000001c > > > > > > The problem is that aes_enc_block() and aes_dec_block() use %rbp as a > > > temporary register, which breaks stack traces if an interrupt occurs. > > > > > > Fix this by replacing %rbp with %r9, which was being used to hold the > > > saved value of %rbp. This required rearranging the AES round macro > > > slightly since %r9d cannot be used as the target of a move from %ah-%dh. > > > > > > Performance is essentially unchanged --- actually about 0.2% faster than > > > before. Interestingly, I also measured aes-generic as being nearly 7% > > > faster than aes-asm, so perhaps aes-asm has outlived its usefulness... > > > > > > Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> > > > > Reviewed-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> > > > > Hmm, it looks like a number of other algorithms in arch/x86/crypto/ use %rbp (or > %ebp), e.g. blowfish, camellia, cast5, and aes-i586. Presumably they have the > same problem. I'm a little confused: do these all need to be fixed, and > when/why did this start being considered broken? This warning was only recently added, with the goal of flushing out these types of issues with hand-coded asm to make frame pointer based stack traces more reliable. I can take a look at fixing the rest of them if you want. -- Josh
