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From: Dave Hansen <dave.hansen@intel.com>
To: "Bae, Chang Seok" <chang.seok.bae@intel.com>
Cc: "Lutomirski, Andy" <luto@kernel.org>,
	Borislav Petkov <bp@suse.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>, X86 ML <x86@kernel.org>,
	"Brown, Len" <len.brown@intel.com>,
	"Liu, Jing2" <jing2.liu@intel.com>,
	"Shankar, Ravi V" <ravi.v.shankar@intel.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v5 14/28] x86/fpu/xstate: Prevent unauthorised use of dynamic user state
Date: Tue, 29 Jun 2021 11:50:56 -0700	[thread overview]
Message-ID: <842d8e8a-44c6-a8c5-c580-a77fc52d267f@intel.com> (raw)
In-Reply-To: <406DB587-F598-484F-A128-990E2DB6EC78@intel.com>

On 6/29/21 11:35 AM, Bae, Chang Seok wrote:
>         if (likely(use_xsave())) {
> +               /*
> +                * MSR IA32_XFD write follows after this XSAVE(S). So if a
> +                * state component is in use, XFD should not be armed for
> +                * current. But, for potential changes in the future,
> +                * cross-check XINUSE and XFD values. If a XINUSE state
> +                * is XFD-armed, the following XSAVE(S) does not save the
> +                * state.
> +                *
> +                * Reference the shadow XFD value instead of reading the
> +                * MSR.
> +                */
> +               if (xfd_capable() && boot_cpu_has(X86_FEATURE_XGETBV1)) {
> +                       u64 current_xfd = (fpu->state_mask & xfd_capable()) ^ xfd_capable();
> +
> +                       WARN_ON_FPU(xgetbv(1) & current_xfd);
> +               }

The code looks fine.  But, as usual, I hate the comment.  Maybe:

		/*
		 * If XFD is armed for an xfeature, XSAVE* will not save
		 * its state.  Ensure XFD is clear for all features that
		 * are in use before XSAVE*.
		 */

BTW, the ->state_mask calculation is a little confusing to me.  I
understand that fpu->state_mask shouldn't have any bits set that are
unset in xgetbv(1).

This code seems to be asking the question: Are any dynamic features in
their init state *and* XFD-armed?

Is it actually important to make sure that they are dynamic features?
Is there *any* case where a feature (dynamic or not) can have XFD armed
and be out of its init state?

  reply	other threads:[~2021-06-29 18:51 UTC|newest]

Thread overview: 75+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-23 19:32 [PATCH v5 00/28] x86: Support Intel Advanced Matrix Extensions Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 01/28] x86/fpu/xstate: Modify the initialization helper to handle both static and dynamic buffers Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 02/28] x86/fpu/xstate: Modify state copy helpers " Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 03/28] x86/fpu/xstate: Modify address finders " Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 04/28] x86/fpu/xstate: Modify the context restore helper " Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 05/28] x86/fpu/xstate: Add a new variable to indicate dynamic user states Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 06/28] x86/fpu/xstate: Add new variables to indicate dynamic xstate buffer size Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 07/28] x86/fpu/xstate: Calculate and remember dynamic xstate buffer sizes Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 08/28] x86/fpu/xstate: Convert the struct fpu 'state' field to a pointer Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 09/28] x86/fpu/xstate: Introduce helpers to manage the xstate buffer dynamically Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 10/28] x86/fpu/xstate: Define the scope of the initial xstate data Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 11/28] x86/fpu/xstate: Update the xstate save function to support dynamic states Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 12/28] x86/fpu/xstate: Update the xstate buffer address finder " Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 13/28] x86/fpu/xstate: Update the xstate context copy function " Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 14/28] x86/fpu/xstate: Prevent unauthorised use of dynamic user state Chang S. Bae
2021-06-16 16:17   ` Dave Hansen
2021-06-16 16:27   ` Dave Hansen
2021-06-16 18:12     ` Andy Lutomirski
2021-06-16 18:47       ` Bae, Chang Seok
2021-06-16 19:01         ` Dave Hansen
2021-06-16 19:23           ` Bae, Chang Seok
2021-06-16 19:28             ` Dave Hansen
2021-06-16 19:37               ` Bae, Chang Seok
2021-06-28 10:11               ` Liu, Jing2
2021-06-29 17:43           ` Bae, Chang Seok
2021-06-29 17:54             ` Dave Hansen
2021-06-29 18:35               ` Bae, Chang Seok
2021-06-29 18:50                 ` Dave Hansen [this message]
2021-06-29 19:13                   ` Bae, Chang Seok
2021-06-29 19:26                     ` Dave Hansen
2021-05-23 19:32 ` [PATCH v5 15/28] x86/arch_prctl: Create ARCH_GET_XSTATE/ARCH_PUT_XSTATE Chang S. Bae
2021-05-24 23:10   ` Len Brown
2021-05-25 17:27     ` Borislav Petkov
2021-05-25 17:33       ` Dave Hansen
2021-05-26  0:38     ` Len Brown
2021-05-27 11:14       ` second, sync-alloc syscall Borislav Petkov
2021-05-27 13:59         ` Len Brown
2021-05-27 19:35           ` Andy Lutomirski
2021-05-25 15:46   ` [PATCH v5 15/28] x86/arch_prctl: Create ARCH_GET_XSTATE/ARCH_PUT_XSTATE Dave Hansen
2021-05-23 19:32 ` [PATCH v5 16/28] x86/fpu/xstate: Support ptracer-induced xstate buffer expansion Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 17/28] x86/fpu/xstate: Adjust the XSAVE feature table to address gaps in state component numbers Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 18/28] x86/fpu/xstate: Disable xstate support if an inconsistent state is detected Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 19/28] x86/cpufeatures/amx: Enumerate Advanced Matrix Extension (AMX) feature bits Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 20/28] x86/fpu/amx: Define AMX state components and have it used for boot-time checks Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 21/28] x86/fpu/amx: Initialize child's AMX state Chang S. Bae
2021-05-24  3:09   ` Andy Lutomirski
2021-05-24 17:37     ` Len Brown
2021-05-24 18:13       ` Andy Lutomirski
2021-05-24 18:21         ` Len Brown
2021-05-25  3:44           ` Andy Lutomirski
2021-05-23 19:32 ` [PATCH v5 22/28] x86/fpu/amx: Enable the AMX feature in 64-bit mode Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 23/28] selftest/x86/amx: Test cases for the AMX state management Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 24/28] x86/fpu/xstate: Use per-task xstate mask for saving xstate in signal frame Chang S. Bae
2021-05-24  3:15   ` Andy Lutomirski
2021-05-24 18:06     ` Len Brown
2021-05-25  4:47       ` Andy Lutomirski
2021-05-25 14:04         ` Len Brown
2021-05-23 19:32 ` [PATCH v5 25/28] x86/fpu/xstate: Skip writing zeros to signal frame for dynamic user states if in INIT-state Chang S. Bae
2021-05-24  3:25   ` Andy Lutomirski
2021-05-24 18:15     ` Len Brown
2021-05-24 18:29       ` Dave Hansen
2021-05-25  4:46       ` Andy Lutomirski
2021-05-23 19:32 ` [PATCH v5 26/28] selftest/x86/amx: Test case for AMX state copy optimization in signal delivery Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 27/28] x86/insn/amx: Add TILERELEASE instruction to the opcode map Chang S. Bae
2021-05-23 19:32 ` [PATCH v5 28/28] x86/fpu/amx: Clear the AMX state when appropriate Chang S. Bae
2021-05-24  3:13   ` Andy Lutomirski
2021-05-24 14:10     ` Dave Hansen
2021-05-24 17:32       ` Len Brown
2021-05-24 17:39         ` Dave Hansen
2021-05-24 18:24           ` Len Brown
2021-05-27 11:56             ` Peter Zijlstra
2021-05-27 14:02               ` Len Brown
2021-05-24 14:06   ` Dave Hansen
2021-05-24 17:34     ` Len Brown
2021-05-24 21:11       ` [PATCH v5-fix " Chang S. Bae

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