linux-kernel - Re: [PATCH 9/9] x86/virt/tdx: Don't initialize module that doesn't support NO_RBP

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Date: Tue, 18 Jun 2024 18:12:13 +0300
From: Nikolay Borisov <nik.borisov@...e.com>
To: Kai Huang <kai.huang@...el.com>, linux-kernel@...r.kernel.org
Cc: x86@...nel.org, dave.hansen@...el.com, dan.j.williams@...el.com,
 kirill.shutemov@...ux.intel.com, rick.p.edgecombe@...el.com,
 peterz@...radead.org, tglx@...utronix.de, bp@...en8.de, mingo@...hat.com,
 hpa@...or.com, seanjc@...gle.com, pbonzini@...hat.com, kvm@...r.kernel.org,
 isaku.yamahata@...el.com, binbin.wu@...ux.intel.com
Subject: Re: [PATCH 9/9] x86/virt/tdx: Don't initialize module that doesn't
 support NO_RBP_MOD feature



On 16.06.24 г. 15:01 ч., Kai Huang wrote:
> Old TDX modules can clobber RBP in the TDH.VP.ENTER SEAMCALL.  However
> RBP is used as frame pointer in the x86_64 calling convention, and
> clobbering RBP could result in bad things like being unable to unwind
> the stack if any non-maskable exceptions (NMI, #MC etc) happens in that
> gap.
> 
> A new "NO_RBP_MOD" feature was introduced to more recent TDX modules to
> not clobber RBP.  This feature is reported in the TDX_FEATURES0 global
> metadata field via bit 18.
> 
> Don't initialize the TDX module if this feature is not supported [1].
> 
> Link: https://lore.kernel.org/all/c0067319-2653-4cbd-8fee-1ccf21b1e646@suse.com/T/#mef98469c51e2382ead2c537ea189752360bd2bef [1]
> Signed-off-by: Kai Huang <kai.huang@...el.com>

Reviewed-by: Nikolay Borisov <nik.borisov@...e.com>