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Date:   Thu, 27 Jul 2023 15:48:26 +0300
From:   kirill.shutemov@linux.intel.com
To:     Kai Huang <kai.huang@intel.com>
Cc:     peterz@infradead.org, linux-kernel@vger.kernel.org,
        dave.hansen@intel.com, tglx@linutronix.de, bp@alien8.de,
        mingo@redhat.com, hpa@zytor.com, x86@kernel.org, seanjc@google.com,
        pbonzini@redhat.com, isaku.yamahata@intel.com,
        sathyanarayanan.kuppuswamy@linux.intel.com,
        n.borisov.lkml@gmail.com
Subject: Re: [PATCH v3 01/12] x86/tdx: Zero out the missing RSI in
 TDX_HYPERCALL macro
Message-ID: <20230727124826.obblw2vtkavr4f2o@box.shutemov.name>
References: <cover.1690369495.git.kai.huang@intel.com>
 <a451f3aecf53d463246a6fa4d322791ade4a78e7.1690369495.git.kai.huang@intel.com>
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On Wed, Jul 26, 2023 at 11:25:03PM +1200, Kai Huang wrote:
> In the TDX_HYPERCALL asm, after the TDCALL instruction returns from the
> untrusted VMM, the registers that the TDX guest shares to the VMM need
> to be cleared to avoid speculative execution of VMM-provided values.
> 
> RSI is specified in the bitmap of those registers, but it is missing
> when zeroing out those registers in the current TDX_HYPERCALL.
> 
> It was there when it was originally added in commit 752d13305c78
> ("x86/tdx: Expand __tdx_hypercall() to handle more arguments"), but was
> later removed in commit 1e70c680375a ("x86/tdx: Do not corrupt
> frame-pointer in __tdx_hypercall()"), which was correct because %rsi is
> later restored in the "pop %rsi".  However a later commit 7a3a401874be
> ("x86/tdx: Drop flags from __tdx_hypercall()") removed that "pop %rsi"
> but forgot to add the "xor %rsi, %rsi" back.
> 
> Fix by adding it back.
> 
> Fixes: 7a3a401874be ("x86/tdx: Drop flags from __tdx_hypercall()")
> Signed-off-by: Kai Huang <kai.huang@intel.com>
> Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov