netdev - Re: [Patch v3 05/14] x86/mm: Handle decryption/re-encryption of bss

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]

Date:   Mon, 28 Nov 2022 08:15:58 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Dexuan Cui <decui@...rosoft.com>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "hpa@...or.com" <hpa@...or.com>, KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "luto@...nel.org" <luto@...nel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "lpieralisi@...nel.org" <lpieralisi@...nel.org>,
        "robh@...nel.org" <robh@...nel.org>, "kw@...ux.com" <kw@...ux.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "hch@...radead.org" <hch@...radead.org>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "brijesh.singh@....com" <brijesh.singh@....com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "isaku.yamahata@...el.com" <isaku.yamahata@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "jane.chu@...cle.com" <jane.chu@...cle.com>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>
Subject: Re: [Patch v3 05/14] x86/mm: Handle decryption/re-encryption of
 bss_decrypted consistently

On 11/27/22 20:52, Dexuan Cui wrote:
>> From: Michael Kelley (LINUX) <mikelley@...rosoft.com>
>> Sent: Thursday, November 17, 2022 6:56 PM
>> [...]
>>
>> But I had not thought about TDX.  In the TDX case, it appears that
>> sme_postprocess_startup() will not decrypt the bss_decrypted section.
>> The corresponding mem_encrypt_free_decrypted_mem() is a no-op unless
>> CONFIG_AMD_MEM_ENCRYPT is set.  But maybe if someone builds a
>> kernel image that supports both TDX and AMD encryption, it could break
>> at runtime on a TDX system.  I would also note that on a TDX system
>> without CONFIG_AMD_MEM_ENCRYPT, the unused memory in the
>> bss_decrypted section never gets freed.
> 
> On a TDX system *with* CONFIG_AMD_MEM_ENCRYPT, the unused
> memory in the bss_decrypted section also never gets freed due to the
> below "return;"
> 
> I'd suggest a Fixes tag should be added to make sure the distro vendors
> notice the patch and backport it :-)
> 
> BTW, I just posted a similar patch as I didn't notice this patch. I have
> replied to my patch email, asking people to ignore my patch.
> 
> Fixes: b3f0907c71e0 ("x86/mm: Add .bss..decrypted section to hold shared variables")

I think the Fixes: tag should really be:

e9d1d2bb75b2 ("treewide: Replace the use of mem_encrypt_active() with cc_platform_has()")

since mem_encrypt_active() used to return sme_me_mask, so the checks were
balanced at that point.

Thanks,
Tom

> 
> void __init mem_encrypt_free_decrypted_mem(void)
> {
>          unsigned long vaddr, vaddr_end, npages;
>          int r;
> 
>          vaddr = (unsigned long)__start_bss_decrypted_unused;
>          vaddr_end = (unsigned long)__end_bss_decrypted;
>          npages = (vaddr_end - vaddr) >> PAGE_SHIFT;
> 
>          /*
>           * The unused memory range was mapped decrypted, change the encryption
>           * attribute from decrypted to encrypted before freeing it.
>           */
>          if (cc_platform_has(CC_ATTR_MEM_ENCRYPT)) {
>                  r = set_memory_encrypted(vaddr, npages);
>                  if (r) {
>                          pr_warn("failed to free unused decrypted pages\n");
>                          return;
>                  }
>          }
> 
>          free_init_pages("unused decrypted", vaddr, vaddr_end);
> }
>