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Mon, 21 Jun 2021 10:31:51 -0400 Received: from imap.suse.de (imap-alt.suse-dmz.suse.de [192.168.254.47]) (using TLSv1.2 with cipher ECDHE-ECDSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 435AB1FD3D; Mon, 21 Jun 2021 14:29:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1624285776; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=TPaT3IOkb2sunrGVTVfN8VJ/vllj6Qah6tRHyuYa/Z0=; b=r5yICesIwXbWBwU2CLBGKaoI+osdQb99EK3rcXh34JiNDy6xH9atd8C9SvLE9uHyAS8X1j V2ac5rasSFabMc8K4GEcCFhuv91jueeb4denjeyVNqX/0Ya2VffcIqdD6ueF2aaQEApcTL CHfk4A+idcGbcf0Pi2eDkMxtp6nT2EU= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1624285776; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; 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bh=TPaT3IOkb2sunrGVTVfN8VJ/vllj6Qah6tRHyuYa/Z0=; b=pvEXhobogfNKSF05nvywHryCmVJb3fuunEQLxQxUUDr7Y2WNgkghOpWGubuuxU0WmLhj92 OUlVwz3qF2SaEkCw== Received: from director2.suse.de ([192.168.254.72]) by imap3-int with ESMTPSA id YDI3C1Ci0GAncAAALh3uQQ (envelope-from ); Mon, 21 Jun 2021 14:29:36 +0000 Date: Mon, 21 Jun 2021 16:29:21 +0200 From: Borislav Petkov To: gregkh@linuxfoundation.org, luto@kernel.org Cc: dave.hansen@linux.intel.com, riel@surriel.com, tglx@linutronix.de, stable@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: FAILED: patch "[PATCH] x86/fpu: Invalidate FPU state after a failed XRSTOR from a" failed to apply to 5.4-stable tree Message-ID: References: <162427270623162@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <162427270623162@kroah.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 21, 2021 at 12:51:46PM +0200, gregkh@linuxfoundation.org wrote: > > The patch below does not apply to the 5.4-stable tree. > If someone wants it applied there, or to any other stable or longterm > tree, then please email the backport, including the original git commit > id to . > > thanks, > > greg k-h > > ------------------ original commit in Linus's tree ------------------ > > From d8778e393afa421f1f117471144f8ce6deb6953a Mon Sep 17 00:00:00 2001 > From: Andy Lutomirski > Date: Tue, 8 Jun 2021 16:36:19 +0200 > Subject: [PATCH] x86/fpu: Invalidate FPU state after a failed XRSTOR from a > user buffer > > Both Intel and AMD consider it to be architecturally valid for XRSTOR to > fail with #PF but nonetheless change the register state. The actual > conditions under which this might occur are unclear [1], but it seems > plausible that this might be triggered if one sibling thread unmaps a page > and invalidates the shared TLB while another sibling thread is executing > XRSTOR on the page in question. > > __fpu__restore_sig() can execute XRSTOR while the hardware registers > are preserved on behalf of a different victim task (using the > fpu_fpregs_owner_ctx mechanism), and, in theory, XRSTOR could fail but > modify the registers. > > If this happens, then there is a window in which __fpu__restore_sig() > could schedule out and the victim task could schedule back in without > reloading its own FPU registers. This would result in part of the FPU > state that __fpu__restore_sig() was attempting to load leaking into the > victim task's user-visible state. > > Invalidate preserved FPU registers on XRSTOR failure to prevent this > situation from corrupting any state. > > [1] Frequent readers of the errata lists might imagine "complex > microarchitectural conditions". > > Fixes: 1d731e731c4c ("x86/fpu: Add a fastpath to __fpu__restore_sig()") > Signed-off-by: Andy Lutomirski > Signed-off-by: Thomas Gleixner > Signed-off-by: Borislav Petkov > Acked-by: Dave Hansen > Acked-by: Rik van Riel > Cc: stable@vger.kernel.org > Link: https://lkml.kernel.org/r/20210608144345.758116583@linutronix.de > > diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c > index d5bc96a536c2..4ab9aeb9a963 100644 > --- a/arch/x86/kernel/fpu/signal.c > +++ b/arch/x86/kernel/fpu/signal.c > @@ -369,6 +369,25 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size) > fpregs_unlock(); > return 0; > } > + > + /* > + * The above did an FPU restore operation, restricted to > + * the user portion of the registers, and failed, but the > + * microcode might have modified the FPU registers > + * nevertheless. > + * > + * If the FPU registers do not belong to current, then > + * invalidate the FPU register state otherwise the task might > + * preempt current and return to user space with corrupted > + * FPU registers. > + * > + * In case current owns the FPU registers then no further > + * action is required. The fixup below will handle it > + * correctly. > + */ > + if (test_thread_flag(TIF_NEED_FPU_LOAD)) > + __cpu_invalidate_fpregs_state(); > + > fpregs_unlock(); > } else { So I'm looking at this and 5.4.127 has: if (!ret) { fpregs_mark_activate(); fpregs_unlock(); return 0; } fpregs_deactivate(fpu); <--- fpregs_unlock(); i.e., an unconditional fpu invalidation there. Which got removed by: 98265c17efa9 ("x86/fpu/xstate: Preserve supervisor states for the slow path in __fpu__restore_sig()") in 5.7. so that Fixes: commit above which points to a 5.1 kernel is probably wrong-ish. amluto? -- Regards/Gruss, Boris. SUSE Software Solutions Germany GmbH, GF: Felix Imendörffer, HRB 36809, AG Nürnberg