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Date: Mon, 11 Feb 2019 10:45:26 -0800
From: Nadav Amit <nadav.amit@...il.com>
To: Borislav Petkov <bp@...en8.de>
Cc: Rick Edgecombe <rick.p.edgecombe@...el.com>,
Andy Lutomirski <luto@...nel.org>,
Ingo Molnar <mingo@...hat.com>,
LKML <linux-kernel@...r.kernel.org>,
X86 ML <x86@...nel.org>,
"H. Peter Anvin" <hpa@...or.com>,
Thomas Gleixner <tglx@...utronix.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Peter Zijlstra <peterz@...radead.org>,
Damian Tometzki <linux_dti@...oud.com>,
linux-integrity <linux-integrity@...r.kernel.org>,
LSM List <linux-security-module@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Linux-MM <linux-mm@...ck.org>,
Will Deacon <will.deacon@....com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Kristen Carlson Accardi <kristen@...ux.intel.com>,
"Dock, Deneen T" <deneen.t.dock@...el.com>,
Kees Cook <keescook@...omium.org>,
Dave Hansen <dave.hansen@...el.com>,
Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH v2 10/20] x86: avoid W^X being broken during modules
loading
> On Feb 11, 2019, at 10:29 AM, Borislav Petkov <bp@...en8.de> wrote:
>
>> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
>> index 76d482a2b716..69f3e650ada8 100644
>> --- a/arch/x86/kernel/alternative.c
>> +++ b/arch/x86/kernel/alternative.c
>> @@ -667,15 +667,29 @@ void __init alternative_instructions(void)
>> * handlers seeing an inconsistent instruction while you patch.
>> */
>> void *__init_or_module text_poke_early(void *addr, const void *opcode,
>> - size_t len)
>> + size_t len)
>> {
>> unsigned long flags;
>> - local_irq_save(flags);
>> - memcpy(addr, opcode, len);
>> - local_irq_restore(flags);
>> - sync_core();
>> - /* Could also do a CLFLUSH here to speed up CPU recovery; but
>> - that causes hangs on some VIA CPUs. */
>> +
>> + if (static_cpu_has(X86_FEATURE_NX) &&
>
> Not a fast path - boot_cpu_has() is fine here.
Are you sure about that? This path is still used when modules are loaded.
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