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Date: Tue, 25 Aug 2020 12:19:39 -0700 From: Dave Hansen <dave.hansen@...el.com> To: "Yu, Yu-cheng" <yu-cheng.yu@...el.com>, Andy Lutomirski <luto@...nel.org> Cc: X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, LKML <linux-kernel@...r.kernel.org>, "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>, Linux-MM <linux-mm@...ck.org>, linux-arch <linux-arch@...r.kernel.org>, Linux API <linux-api@...r.kernel.org>, Arnd Bergmann <arnd@...db.de>, Balbir Singh <bsingharora@...il.com>, Borislav Petkov <bp@...en8.de>, Cyrill Gorcunov <gorcunov@...il.com>, Dave Hansen <dave.hansen@...ux.intel.com>, Eugene Syromiatnikov <esyr@...hat.com>, Florian Weimer <fweimer@...hat.com>, "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>, Kees Cook <keescook@...omium.org>, Mike Kravetz <mike.kravetz@...cle.com>, Nadav Amit <nadav.amit@...il.com>, Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>, Peter Zijlstra <peterz@...radead.org>, Randy Dunlap <rdunlap@...radead.org>, "Ravi V. Shankar" <ravi.v.shankar@...el.com>, Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>, Dave Martin <Dave.Martin@....com>, Weijiang Yang <weijiang.yang@...el.com> Subject: Re: [PATCH v11 25/25] x86/cet/shstk: Add arch_prctl functions for shadow stack On 8/25/20 11:43 AM, Yu, Yu-cheng wrote: >>> arch_prctl(ARCH_X86_CET_MMAP_SHSTK, u64 *args) >>> Allocate a new shadow stack. >>> >>> The parameter 'args' is a pointer to a user buffer. >>> >>> *args = desired size >>> *(args + 1) = MAP_32BIT or MAP_POPULATE >>> >>> On returning, *args is the allocated shadow stack address. >> >> This is hideous. Would this be better as a new syscall? > > Could you point out why this is hideous, so that I can modify the > arch_prctl? Passing values in memory is hideous when we don't have to. A syscall would let you have separate arguments for size and flags and would also let you have a nice return value instead of needing to do that in memory too. > I think this is more arch-specific. Even if it becomes a new syscall, > we still need to pass the same parameters. Right, but without the copying in and out of memory.
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