linux-kernel - Re: [PATCH v2 08/25] x86/virt/tdx: Add SEAMCALL wrappers for TDX page cache management

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <b3bdd85c-9373-483a-a205-631016a3a77d@intel.com>
Date: Fri, 1 Nov 2024 12:33:26 +1300
From: "Huang, Kai" <kai.huang@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>, "Hansen, Dave"
	<dave.hansen@...el.com>, "Zhao, Yan Y" <yan.y.zhao@...el.com>
CC: "sean.j.christopherson@...el.com" <sean.j.christopherson@...el.com>,
	"seanjc@...gle.com" <seanjc@...gle.com>, "binbin.wu@...ux.intel.com"
	<binbin.wu@...ux.intel.com>, "Yao, Yuan" <yuan.yao@...el.com>, "Li, Xiaoyao"
	<xiaoyao.li@...el.com>, "isaku.yamahata@...il.com"
	<isaku.yamahata@...il.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "tony.lindgren@...ux.intel.com"
	<tony.lindgren@...ux.intel.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>, "Chatre, Reinette"
	<reinette.chatre@...el.com>, "Yamahata, Isaku" <isaku.yamahata@...el.com>
Subject: Re: [PATCH v2 08/25] x86/virt/tdx: Add SEAMCALL wrappers for TDX page
 cache management



On 1/11/2024 7:57 am, Edgecombe, Rick P wrote:
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index bad83f6a3b0c..bb7cdb867581 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c

...

> +static void tdx_clear_page(unsigned long page_pa)
> +{
> +       const void *zero_page = (const void *) __va(page_to_phys(ZERO_PAGE(0)));
> +       void *page = __va(page_pa);
> +       unsigned long i;
> +
> +       /*
> +        * The page could have been poisoned.  MOVDIR64B also clears
> +        * the poison bit so the kernel can safely use the page again.
> +        */
> +       for (i = 0; i < PAGE_SIZE; i += 64)
> +               movdir64b(page + i, zero_page);
> +       /*
> +        * MOVDIR64B store uses WC buffer.  Prevent following memory reads
> +        * from seeing potentially poisoned cache.
> +        */
> +       __mb();
> +}

Just FYI there's already one reset_tdx_pages() doing the same thing in 
x86 tdx.c:

/*
  * Convert TDX private pages back to normal by using MOVDIR64B to
  * clear these pages.  Note this function doesn't flush cache of
  * these TDX private pages.  The caller should make sure of that.
  */
static void reset_tdx_pages(unsigned long base, unsigned long size)
{
         const void *zero_page = (const void *)page_address(ZERO_PAGE(0));
         unsigned long phys, end;

         end = base + size;
         for (phys = base; phys < end; phys += 64)
                 movdir64b(__va(phys), zero_page);

         /*
          * MOVDIR64B uses WC protocol.  Use memory barrier to
          * make sure any later user of these pages sees the
          * updated data.
          */
         mb();
}