Date: Fri, 26 Jan 2018 09:40:23 -0800 From: Linus Torvalds <torvalds@...ux-foundation.org> To: Andy Lutomirski <luto@...nel.org> Cc: Alan Cox <alan@...ux.intel.com>, David Laight <David.Laight@...lab.com>, "the arch/x86 maintainers" <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jann Horn <jannh@...gle.com>, Samuel Neves <samuel.c.p.neves@...il.com>, Dan Williams <dan.j.williams@...el.com>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, Borislav Petkov <bp@...en8.de> Subject: Re: [PATCH] x86/retpoline/entry: Disable the entire SYSCALL64 fast path with retpolines on On Fri, Jan 26, 2018 at 7:57 AM, Andy Lutomirski <luto@...nel.org> wrote: > > I gave the rearrangement like this a try yesterday and it's a bit of a > mess. Part of the problem is that there are a bunch of pieces of code > that expect sys_xyz() to be actual callable functions. That's not supposed to be a mess. That's part of why we do that whole indirection through SYSC##xyz to sys##_xyz: the asm-callable ones will do the full casting of troublesome arguments (some architectures have C calling sequence rules that have security issues, so we need to make sure that the arguments actually follow the right rules and 'int' arguments are properly sign-extended etc). So that whole indirection could be made to *also* create another version of the syscall that instead took the arguments from ptregs. We already do exactly that for the tracing events: look how FTRACE_SYSCALLS ends up creating that extra metadata. The ptreg version should be done the same way: don't make 'sys_xyz()' take a struct ptregs, instead make those SYSCALL_DEFINE*() macros create a _new_ function called 'ptregs_xyz()' and then that function does the argument unpacking. Then the x86 system call table can just be switched over to call those ptreg versions instead. Linus
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