linux-kernel - Re: [PATCH Part1 v5 17/38] x86/mm: Add support to validate memory when changing C-bit

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Date:   Wed, 25 Aug 2021 13:06:06 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andi Kleen <ak@...ux.intel.com>, tony.luck@...el.com,
        marcorr@...gle.com, sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH Part1 v5 17/38] x86/mm: Add support to validate memory
 when changing C-bit

On Fri, Aug 20, 2021 at 10:19:12AM -0500, Brijesh Singh wrote:
> +	while (hdr->cur_entry <= hdr->end_entry) {
> +		ghcb_set_sw_scratch(ghcb, (u64)__pa(data));
> +
> +		ret = sev_es_ghcb_hv_call(ghcb, NULL, SVM_VMGEXIT_PSC, 0, 0);
> +
> +		/*
> +		 * Page State Change VMGEXIT can pass error code through
> +		 * exit_info_2.
> +		 */
> +		if (WARN(ret || ghcb->save.sw_exit_info_2,
> +			 "SEV-SNP: PSC failed ret=%d exit_info_2=%llx\n",
> +			 ret, ghcb->save.sw_exit_info_2)) {
> +			ret = 1;
> +			goto out;
> +		}
> +
> +		/*
> +		 * Sanity check that entry processing is not going backward.
> +		 * This will happen only if hypervisor is tricking us.
> +		 */
> +		if (WARN(hdr->end_entry > end_entry || cur_entry > hdr->cur_entry,
> +			 "SEV-SNP:  PSC processing going backward, end_entry %d (got %d) cur_entry %d (got %d)\n",

I really meant putting the beginning of that string at the very first
position on the line:

                if (WARN(hdr->end_entry > end_entry || cur_entry > hdr->cur_entry,
"SEV-SNP: PSC processing going backward, end_entry %d (got %d) cur_entry %d (got %d)\n",
                         end_entry, hdr->end_entry, cur_entry, hdr->cur_entry)) {

Exactly like this!

...

> +static void set_page_state(unsigned long vaddr, unsigned int npages, int op)
> +{
> +	unsigned long vaddr_end, next_vaddr;
> +	struct snp_psc_desc *desc;
> +
> +	vaddr = vaddr & PAGE_MASK;
> +	vaddr_end = vaddr + (npages << PAGE_SHIFT);
> +
> +	desc = kmalloc(sizeof(*desc), GFP_KERNEL_ACCOUNT);

And again, from previous review:

kzalloc() so that you don't have to memset() later in
__set_page_state().

> +	if (!desc)
> +		panic("SEV-SNP: failed to alloc memory for PSC descriptor\n");

"allocate" fits just fine too.

> +
> +	while (vaddr < vaddr_end) {
> +		/*
> +		 * Calculate the last vaddr that can be fit in one
> +		 * struct snp_psc_desc.
> +		 */
> +		next_vaddr = min_t(unsigned long, vaddr_end,
> +				   (VMGEXIT_PSC_MAX_ENTRY * PAGE_SIZE) + vaddr);
> +
> +		__set_page_state(desc, vaddr, next_vaddr, op);
> +
> +		vaddr = next_vaddr;
> +	}
> +
> +	kfree(desc);
> +}

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette