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From: Dave Hansen <dave.hansen@intel.com>
To: kernel-hardening@lists.openwall.com
Cc: keescook@chromium.org,
	Elena Reshetova <elena.reshetova@intel.com>,
	Hans Liljestrand <ishkamiel@gmail.com>,
	David Windsor <dwindsor@gmail.com>
Subject: Re: [kernel-hardening] [RFC PATCH 12/13] x86: x86 implementation for HARDENED_ATOMIC
Date: Mon, 3 Oct 2016 12:27:01 -0700	[thread overview]
Message-ID: <57F2B105.9050400@intel.com> (raw)
In-Reply-To: <1475476886-26232-13-git-send-email-elena.reshetova@intel.com>

On 10/02/2016 11:41 PM, Elena Reshetova wrote:
>  static __always_inline void atomic_add(int i, atomic_t *v)
>  {
> -	asm volatile(LOCK_PREFIX "addl %1,%0"
> +	asm volatile(LOCK_PREFIX "addl %1,%0\n"
> +
> +#ifdef CONFIG_HARDENED_ATOMIC
> +		     "jno 0f\n"
> +		     LOCK_PREFIX "subl %1,%0\n"
> +		     "int $4\n0:\n"
> +		     _ASM_EXTABLE(0b, 0b)
> +#endif
> +
> +		     : "+m" (v->counter)
> +		     : "ir" (i));
> +}

Rather than doing all this assembly and exception stuff, could we just do:

static __always_inline void atomic_add(int i, atomic_t *v)
{
	if (atomic_add_unless(v, a, INT_MAX))
		BUG_ON_OVERFLOW_FOO()...
}

That way, there's also no transient state where somebody can have
observed the overflow before it is fixed up.  Granted, this
cmpxchg-based operation _is_ more expensive than the fast-path locked addl.

  parent reply	other threads:[~2016-10-03 19:27 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-10-03  6:41 [kernel-hardening] [RFC PATCH 00/13] HARDENING_ATOMIC feature Elena Reshetova
2016-10-03  6:41 ` [kernel-hardening] [RFC PATCH 01/13] Add architecture independent hardened atomic base Elena Reshetova
2016-10-03 21:10   ` [kernel-hardening] " Kees Cook
2016-10-03 21:26     ` David Windsor
2016-10-03 21:38       ` Kees Cook
2016-10-04  7:05         ` [kernel-hardening] " Reshetova, Elena
2016-10-05 15:37           ` [kernel-hardening] " Dave Hansen
2016-10-04  7:07         ` [kernel-hardening] " Reshetova, Elena
2016-10-04  6:54       ` Reshetova, Elena
2016-10-04  7:23       ` Reshetova, Elena
2016-10-12  8:26     ` [kernel-hardening] " AKASHI Takahiro
2016-10-12 17:25       ` Reshetova, Elena
2016-10-12 22:50         ` Kees Cook
2016-10-13 14:31           ` Hans Liljestrand
2016-10-03  6:41 ` [kernel-hardening] [RFC PATCH 02/13] percpu-refcount: leave atomic counter unprotected Elena Reshetova
2016-10-03 21:12   ` [kernel-hardening] " Kees Cook
2016-10-04  6:24     ` [kernel-hardening] " Reshetova, Elena
2016-10-04 13:06       ` [kernel-hardening] " Hans Liljestrand
2016-10-03  6:41 ` [kernel-hardening] [RFC PATCH 03/13] kernel: identify wrapping atomic usage Elena Reshetova
2016-10-03 21:13   ` [kernel-hardening] " Kees Cook
2016-10-04  6:28     ` [kernel-hardening] " Reshetova, Elena
2016-10-03  6:41 ` [kernel-hardening] [RFC PATCH 04/13] mm: " Elena Reshetova
2016-10-03  6:41 ` [kernel-hardening] [RFC PATCH 05/13] fs: " Elena Reshetova
2016-10-03 21:57   ` Jann Horn
2016-10-03 22:21     ` Kees Cook
2016-10-03  6:41 ` [kernel-hardening] [RFC PATCH 06/13] net: " Elena Reshetova
2016-10-03  6:41 ` [kernel-hardening] [RFC PATCH 07/13] net: atm: " Elena Reshetova
2016-10-03  6:41 ` [kernel-hardening] [RFC PATCH 08/13] security: " Elena Reshetova
2016-10-03  6:41 ` [kernel-hardening] [RFC PATCH 09/13] drivers: identify wrapping atomic usage (part 1/2) Elena Reshetova
2016-10-03  6:41 ` [kernel-hardening] [RFC PATCH 10/13] drivers: identify wrapping atomic usage (part 2/2) Elena Reshetova
2016-10-03  6:41 ` [kernel-hardening] [RFC PATCH 11/13] x86: identify wrapping atomic usage Elena Reshetova
2016-10-03  6:41 ` [kernel-hardening] [RFC PATCH 12/13] x86: x86 implementation for HARDENED_ATOMIC Elena Reshetova
2016-10-03  9:47   ` Jann Horn
2016-10-04  7:15     ` Reshetova, Elena
2016-10-04 12:46       ` Jann Horn
2016-10-03 19:27   ` Dave Hansen [this message]
2016-10-03 22:49     ` David Windsor
2016-10-04 12:41     ` Jann Horn
2016-10-04 18:51       ` Kees Cook
2016-10-04 19:48         ` Jann Horn
2016-10-05 15:39       ` Dave Hansen
2016-10-05 16:18         ` Jann Horn
2016-10-05 16:32           ` Dave Hansen
2016-10-03 21:29   ` [kernel-hardening] " Kees Cook
2016-10-03  6:41 ` [kernel-hardening] [RFC PATCH 13/13] lkdtm: add tests for atomic over-/underflow Elena Reshetova
2016-10-03 21:35   ` [kernel-hardening] " Kees Cook
2016-10-04  6:27     ` [kernel-hardening] " Reshetova, Elena
2016-10-04  6:40       ` [kernel-hardening] " Hans Liljestrand
2016-10-03  8:14 ` [kernel-hardening] [RFC PATCH 00/13] HARDENING_ATOMIC feature AKASHI Takahiro
2016-10-03  8:13   ` Reshetova, Elena
2016-10-03 21:01 ` [kernel-hardening] " Kees Cook

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