From: Andy Lutomirski <luto@kernel.org>
To: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
Nadav Amit <nadav.amit@gmail.com>,
Rick Edgecombe <rick.p.edgecombe@intel.com>,
Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@redhat.com>,
LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Damian Tometzki <linux_dti@icloud.com>,
linux-integrity <linux-integrity@vger.kernel.org>,
LSM List <linux-security-module@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Kernel Hardening <kernel-hardening@lists.openwall.com>,
Linux-MM <linux-mm@kvack.org>, Will Deacon <will.deacon@arm.com>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Kristen Carlson Accardi <kristen@linux.intel.com>,
"Dock, Deneen T" <deneen.t.dock@intel.com>,
Kees Cook <keescook@chromium.org>,
Dave Hansen <dave.hansen@intel.com>,
Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [PATCH v2 10/20] x86: avoid W^X being broken during modules loading
Date: Thu, 7 Mar 2019 12:02:13 -0800 [thread overview]
Message-ID: <CALCETrUY6L_Fwd9CZzo2eZL8HT2sBSHFiD-Bp-HCPPFBxkzcdA@mail.gmail.com> (raw)
In-Reply-To: <20190307170629.GG26566@zn.tnic>
On Thu, Mar 7, 2019 at 9:06 AM Borislav Petkov <bp@alien8.de> wrote:
>
> On Thu, Mar 07, 2019 at 08:53:34AM -0800, hpa@zytor.com wrote:
> > If we *do*, what is the issue here? Although boot_cpu_has() isn't
> > slow (it should in general be possible to reduce to one testb
> > instruction followed by a conditional jump) it seems that "avoiding an
> > alternatives slot" *should* be a *very* weak reason, and seems to me
> > to look like papering over some other problem.
>
> Forget the current thread: this is simply trying to document when to use
> static_cpu_has() and when to use boot_cpu_has(). I get asked about it at
> least once a month.
>
> And then it is replacing clear slow paths using static_cpu_has() with
> boot_cpu_has() because there's purely no need to patch there. And having
> a RIP-relative MOV and a JMP is good enough for slow paths.
>
Should we maybe rename these functions? static_cpu_has() is at least
reasonably obvious. But cpu_feature_enabled() is different for
reasons I've never understood, and boot_cpu_has() is IMO terribly
named. It's not about the boot cpu -- it's about doing the same thing
but with less bloat and less performance.
(And can we maybe collapse cpu_feature_enabled() and static_cpu_has()
into the same function?)
--Andy
next prev parent reply other threads:[~2019-03-07 20:02 UTC|newest]
Thread overview: 83+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-29 0:34 [PATCH v2 00/20] Merge text_poke fixes and executable lockdowns Rick Edgecombe
2019-01-29 0:34 ` [PATCH v2 01/20] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()" Rick Edgecombe
2019-01-29 0:34 ` [PATCH v2 02/20] x86/jump_label: Use text_poke_early() during early init Rick Edgecombe
2019-01-29 0:34 ` [PATCH v2 03/20] x86/mm: temporary mm struct Rick Edgecombe
2019-01-31 11:29 ` Borislav Petkov
2019-01-31 22:19 ` Nadav Amit
2019-02-01 0:08 ` Borislav Petkov
2019-02-01 0:25 ` Nadav Amit
2019-02-04 14:28 ` Borislav Petkov
2019-01-29 0:34 ` [PATCH v2 04/20] fork: provide a function for copying init_mm Rick Edgecombe
2019-02-05 8:53 ` Borislav Petkov
2019-02-05 9:03 ` Nadav Amit
2019-01-29 0:34 ` [PATCH v2 05/20] x86/alternative: initializing temporary mm for patching Rick Edgecombe
2019-02-05 9:18 ` Borislav Petkov
2019-02-11 0:39 ` Nadav Amit
2019-02-11 5:18 ` Andy Lutomirski
2019-02-11 18:04 ` Nadav Amit
2019-02-11 19:07 ` Andy Lutomirski
2019-02-11 19:07 ` Andy Lutomirski
2019-02-11 19:18 ` Nadav Amit
2019-02-11 22:47 ` Andy Lutomirski
2019-02-11 22:47 ` Andy Lutomirski
2019-02-12 18:23 ` Nadav Amit
2019-01-29 0:34 ` [PATCH v2 06/20] x86/alternative: use temporary mm for text poking Rick Edgecombe
2019-02-05 9:58 ` Borislav Petkov
2019-02-05 11:31 ` Peter Zijlstra
2019-02-05 12:35 ` Borislav Petkov
2019-02-05 13:25 ` Peter Zijlstra
2019-02-05 17:54 ` Nadav Amit
2019-02-05 13:29 ` Peter Zijlstra
2019-01-29 0:34 ` [PATCH v2 07/20] x86/kgdb: avoid redundant comparison of patched code Rick Edgecombe
2019-01-29 0:34 ` [PATCH v2 08/20] x86/ftrace: set trampoline pages as executable Rick Edgecombe
2019-01-29 0:34 ` [PATCH v2 09/20] x86/kprobes: instruction pages initialization enhancements Rick Edgecombe
2019-02-11 18:22 ` Borislav Petkov
2019-02-11 19:36 ` Nadav Amit
2019-01-29 0:34 ` [PATCH v2 10/20] x86: avoid W^X being broken during modules loading Rick Edgecombe
2019-02-11 18:29 ` Borislav Petkov
2019-02-11 18:45 ` Nadav Amit
2019-02-11 19:01 ` Borislav Petkov
2019-02-11 19:09 ` Nadav Amit
2019-02-11 19:10 ` Borislav Petkov
2019-02-11 19:27 ` Nadav Amit
2019-02-11 19:42 ` Borislav Petkov
2019-02-11 20:32 ` Nadav Amit
2019-03-07 15:10 ` [PATCH] x86/cpufeature: Remove __pure attribute to _static_cpu_has() Borislav Petkov
2019-03-07 16:43 ` hpa
2019-03-07 17:02 ` Borislav Petkov
2019-03-29 18:22 ` [tip:x86/asm] " tip-bot for Borislav Petkov
2019-03-07 7:29 ` [PATCH v2 10/20] x86: avoid W^X being broken during modules loading Borislav Petkov
2019-03-07 16:53 ` hpa
2019-03-07 17:06 ` Borislav Petkov
2019-03-07 20:02 ` Andy Lutomirski [this message]
2019-03-07 20:02 ` Andy Lutomirski
2019-03-07 20:25 ` Borislav Petkov
2019-01-29 0:34 ` [PATCH v2 11/20] x86/jump-label: remove support for custom poker Rick Edgecombe
2019-02-11 18:37 ` Borislav Petkov
2019-01-29 0:34 ` [PATCH v2 12/20] x86/alternative: Remove the return value of text_poke_*() Rick Edgecombe
2019-01-29 0:34 ` [PATCH v2 13/20] Add set_alias_ function and x86 implementation Rick Edgecombe
2019-02-11 19:09 ` Borislav Petkov
2019-02-11 19:27 ` Edgecombe, Rick P
2019-02-11 19:27 ` Edgecombe, Rick P
2019-02-11 22:59 ` Andy Lutomirski
2019-02-11 22:59 ` Andy Lutomirski
2019-02-12 0:01 ` Edgecombe, Rick P
2019-02-12 0:01 ` Edgecombe, Rick P
2019-01-29 0:34 ` [PATCH v2 14/20] mm: Make hibernate handle unmapped pages Rick Edgecombe
2019-02-19 11:04 ` Borislav Petkov
2019-02-19 11:04 ` Borislav Petkov
2019-02-19 21:28 ` Edgecombe, Rick P
2019-02-19 21:28 ` Edgecombe, Rick P
2019-02-20 16:07 ` Borislav Petkov
2019-02-20 16:07 ` Borislav Petkov
2019-01-29 0:34 ` [PATCH v2 15/20] vmalloc: New flags for safe vfree on special perms Rick Edgecombe
2019-02-19 12:48 ` Borislav Petkov
2019-02-19 19:42 ` Edgecombe, Rick P
2019-02-19 19:42 ` Edgecombe, Rick P
2019-02-20 16:14 ` Borislav Petkov
2019-02-20 16:14 ` Borislav Petkov
2019-01-29 0:34 ` [PATCH v2 16/20] modules: Use vmalloc special flag Rick Edgecombe
2019-01-29 0:34 ` [PATCH v2 17/20] bpf: " Rick Edgecombe
2019-01-29 0:34 ` [PATCH v2 18/20] x86/ftrace: " Rick Edgecombe
2019-01-29 0:34 ` [PATCH v2 19/20] x86/kprobes: " Rick Edgecombe
2019-01-29 0:34 ` [PATCH v2 20/20] x86/alternative: comment about module removal races Rick Edgecombe
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