On Wed, Jan 11, 2017 at 11:05 PM, Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> wrote: > On Tue, Jan 10, 2017 at 09:05:28AM -0800, Linus Torvalds wrote: >> >> I'm pretty sure we have random asm code that may not maintain a >> 16-byte stack alignment when it calls other code (including, in some >> cases, calling C code). >> >> So I'm not at all convinced that this is a good idea. We shouldn't >> expect 16-byte alignment to be something trustworthy. > > So what if we audited all the x86 assembly code to fix this? Would > it then be acceptable to do a 16-byte aligned stack? > > On the face of it it doesn't seem to be a huge amount of code > assuming they mostly live under arch/x86. The problem is that we have nasties like TRACE_IRQS_OFF. Performance doesn't really matter for these macros, so we could probably rig up a helper for forcibly align the stack there. Maybe FRAME_BEGIN_FORCE_ALIGN? I also think I'd rather not to modify pt_regs. We should just fix the small number of code paths that create a pt_regs and then call into C code to align the stack. But if we can't do this with automatic verification, then I'm not sure I want to do it at all. The asm is already more precarious than I'd like, and having a code path that is misaligned is asking for obscure bugs down the road. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
