linux-kernel - Re: [PATCH v3 01/12] x86/tdx: Zero out the missing RSI in TDX

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Date:   Thu, 27 Jul 2023 15:48:26 +0300
From:   kirill.shutemov@...ux.intel.com
To:     Kai Huang <kai.huang@...el.com>
Cc:     peterz@...radead.org, linux-kernel@...r.kernel.org,
        dave.hansen@...el.com, tglx@...utronix.de, bp@...en8.de,
        mingo@...hat.com, hpa@...or.com, x86@...nel.org, seanjc@...gle.com,
        pbonzini@...hat.com, isaku.yamahata@...el.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com,
        n.borisov.lkml@...il.com
Subject: Re: [PATCH v3 01/12] x86/tdx: Zero out the missing RSI in
 TDX_HYPERCALL macro

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@...el.com>
> Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>

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

-- 
  Kiryl Shutsemau / Kirill A. Shutemov