On 10/28/20 11:46 AM, Joerg Roedel wrote:
> From: Joerg Roedel <[email protected]>
>
> 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: Joerg Roedel <[email protected]>
Reviewed-by: Tom Lendacky <[email protected]>
> ---
> arch/x86/kernel/sev-es.c | 20 +++++++++++++-------
> 1 file changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
> index 4a96726fbaf8..0bd1a0fc587e 100644
> --- a/arch/x86/kernel/sev-es.c
> +++ b/arch/x86/kernel/sev-es.c
> @@ -374,8 +374,8 @@ static enum es_result vc_read_mem(struct es_em_ctxt *ctxt,
> return ES_EXCEPTION;
> }
>
> -static bool vc_slow_virt_to_phys(struct ghcb *ghcb, struct es_em_ctxt *ctxt,
> - unsigned long vaddr, phys_addr_t *paddr)
> +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;
> unsigned int level;
> @@ -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;
>