Commit 2411cd82 authored by Joerg Roedel's avatar Joerg Roedel Committed by Borislav Petkov
Browse files

x86/sev-es: Do not support MMIO to/from encrypted memory 



MMIO memory is usually not mapped encrypted, so there is no reason to
support emulated MMIO when it is mapped encrypted.

Prevent a possible hypervisor attack where a RAM page is mapped as
an MMIO page in the nested page-table, so that any guest access to it
will trigger a #VC exception and leak the data on that page to the
hypervisor via the GHCB (like with valid MMIO). On the read side this
attack would allow the HV to inject data into the guest.

Signed-off-by: default avatarJoerg Roedel <jroedel@suse.de>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Reviewed-by: default avatarTom Lendacky <thomas.lendacky@amd.com>
Link: https://lkml.kernel.org/r/20201028164659.27002-6-joro@8bytes.org
parent c9f09539

arch/x86/kernel/sev-es.c

+13 −7
Original line number Diff line number Diff line
@@ -374,7 +374,7 @@ fault: 
	return ES_EXCEPTION;

}



static bool vc_slow_virt_to_phys(struct ghcb *ghcb, struct es_em_ctxt *ctxt,

static enum es_result vc_slow_virt_to_phys(struct ghcb *ghcb, struct es_em_ctxt *ctxt,

					   unsigned long vaddr, phys_addr_t *paddr)

{

	unsigned long va = (unsigned long)vaddr;
@@ -394,15 +394,19 @@ static bool vc_slow_virt_to_phys(struct ghcb *ghcb, struct es_em_ctxt *ctxt, 
		if (user_mode(ctxt->regs))

			ctxt->fi.error_code |= X86_PF_USER;



		return false;

		return ES_EXCEPTION;

	}



	if (WARN_ON_ONCE(pte_val(*pte) & _PAGE_ENC))

		/* Emulated MMIO to/from encrypted memory not supported */

		return ES_UNSUPPORTED;



	pa = (phys_addr_t)pte_pfn(*pte) << PAGE_SHIFT;

	pa |= va & ~page_level_mask(level);



	*paddr = pa;



	return true;

	return ES_OK;

}



/* Include code shared with pre-decompression boot stage */
@@ -731,6 +735,7 @@ static enum es_result vc_do_mmio(struct ghcb *ghcb, struct es_em_ctxt *ctxt, 
{

	u64 exit_code, exit_info_1, exit_info_2;

	unsigned long ghcb_pa = __pa(ghcb);

	enum es_result res;

	phys_addr_t paddr;

	void __user *ref;
@@ -740,11 +745,12 @@ static enum es_result vc_do_mmio(struct ghcb *ghcb, struct es_em_ctxt *ctxt, 


	exit_code = read ? SVM_VMGEXIT_MMIO_READ : SVM_VMGEXIT_MMIO_WRITE;



	if (!vc_slow_virt_to_phys(ghcb, ctxt, (unsigned long)ref, &paddr)) {

		if (!read)

	res = vc_slow_virt_to_phys(ghcb, ctxt, (unsigned long)ref, &paddr);

	if (res != ES_OK) {

		if (res == ES_EXCEPTION && !read)

			ctxt->fi.error_code |= X86_PF_WRITE;



		return ES_EXCEPTION;

		return res;

	}



	exit_info_1 = paddr;

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