From: Nikolay Borisov <nik.borisov@suse.com>
To: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <peterz@infradead.org>,
Josh Poimboeuf <jpoimboe@kernel.org>,
Andy Lutomirski <luto@kernel.org>,
Jonathan Corbet <corbet@lwn.net>,
Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>,
tony.luck@intel.com, ak@linux.intel.com,
tim.c.chen@linux.intel.com
Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
kvm@vger.kernel.org,
Alyssa Milburn <alyssa.milburn@linux.intel.com>,
Daniel Sneddon <daniel.sneddon@linux.intel.com>,
antonio.gomez.iglesias@linux.intel.com,
Alyssa Milburn <alyssa.milburn@intel.com>,
Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH v3 1/6] x86/bugs: Add asm helpers for executing VERW
Date: Thu, 26 Oct 2023 16:44:58 +0300 [thread overview]
Message-ID: <1f756579-8f33-40ca-ae50-4db78c615f60@suse.com> (raw)
In-Reply-To: <20231025-delay-verw-v3-1-52663677ee35@linux.intel.com>
<snip>
> +
> +.pushsection .entry.text, "ax"
> +
> +.align L1_CACHE_BYTES, 0xcc
> +SYM_CODE_START_NOALIGN(mds_verw_sel)
> + UNWIND_HINT_UNDEFINED
> + ANNOTATE_NOENDBR
> + .word __KERNEL_DS
> +SYM_CODE_END(mds_verw_sel);
> +/* For KVM */
> +EXPORT_SYMBOL_GPL(mds_verw_sel);
> +
> +.popsection
<snip>
> diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
> index c55cc243592e..005e69f93115 100644
> --- a/arch/x86/include/asm/nospec-branch.h
> +++ b/arch/x86/include/asm/nospec-branch.h
> @@ -329,6 +329,21 @@
> #endif
> .endm
>
> +/*
> + * Macros to execute VERW instruction that mitigate transient data sampling
> + * attacks such as MDS. On affected systems a microcode update overloaded VERW
> + * instruction to also clear the CPU buffers. VERW clobbers CFLAGS.ZF.
> + *
> + * Note: Only the memory operand variant of VERW clears the CPU buffers.
> + */
> +.macro EXEC_VERW
> + verw _ASM_RIP(mds_verw_sel)
> +.endm
> +
> +.macro CLEAR_CPU_BUFFERS
> + ALTERNATIVE "", __stringify(EXEC_VERW), X86_FEATURE_CLEAR_CPU_BUF
> +.endm
What happened with the first 5 bytes of a 7 byte nop being complemented
by __KERNEL_DS in order to handle VERW being executed after user
registers are restored and having its memory operand ?
> +
> #else /* __ASSEMBLY__ */
>
> #define ANNOTATE_RETPOLINE_SAFE \
>
next prev parent reply other threads:[~2023-10-26 13:45 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-25 20:52 [PATCH v3 0/6] Delay VERW Pawan Gupta
2023-10-25 20:52 ` [PATCH v3 1/6] x86/bugs: Add asm helpers for executing VERW Pawan Gupta
2023-10-25 21:10 ` Andrew Cooper
2023-10-25 21:28 ` Josh Poimboeuf
2023-10-25 21:30 ` Andrew Cooper
2023-10-25 21:49 ` Josh Poimboeuf
2023-10-25 22:07 ` Pawan Gupta
2023-10-25 22:13 ` Andrew Cooper
2023-10-27 13:48 ` Pawan Gupta
2023-10-27 14:12 ` Andrew Cooper
2023-10-27 14:24 ` Pawan Gupta
2023-10-26 13:44 ` Nikolay Borisov [this message]
2023-10-26 13:58 ` Andrew Cooper
2023-10-25 20:52 ` [PATCH v3 2/6] x86/entry_64: Add VERW just before userspace transition Pawan Gupta
2023-10-26 16:25 ` Nikolay Borisov
2023-10-26 19:29 ` Pawan Gupta
2023-10-26 19:40 ` Dave Hansen
2023-10-26 21:15 ` Pawan Gupta
2023-10-26 22:13 ` Pawan Gupta
2023-10-26 22:17 ` Dave Hansen
2023-10-25 20:53 ` [PATCH v3 3/6] x86/entry_32: " Pawan Gupta
2023-10-25 20:53 ` [PATCH v3 4/6] x86/bugs: Use ALTERNATIVE() instead of mds_user_clear static key Pawan Gupta
2023-10-25 20:53 ` [PATCH v3 5/6] KVM: VMX: Use BT+JNC, i.e. EFLAGS.CF to select VMRESUME vs. VMLAUNCH Pawan Gupta
2023-10-25 20:53 ` [PATCH v3 6/6] KVM: VMX: Move VERW closer to VMentry for MDS mitigation Pawan Gupta
2023-10-26 16:14 ` Nikolay Borisov
2023-10-26 19:07 ` Pawan Gupta
2023-10-26 19:30 ` Sean Christopherson
2023-10-26 20:17 ` Sean Christopherson
2023-10-26 21:27 ` Pawan Gupta
2023-10-26 20:48 ` Pawan Gupta
2023-10-26 21:22 ` Sean Christopherson
2023-10-26 22:03 ` Pawan Gupta
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