From: Tom Lendacky <thomas.lendacky@amd.com>
To: Joerg Roedel <joro@8bytes.org>, x86@kernel.org
Cc: Joerg Roedel <jroedel@suse.de>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Kees Cook <keescook@chromium.org>,
Arvind Sankar <nivedita@alum.mit.edu>,
Martin Radev <martin.b.radev@gmail.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 5/5] x86/sev-es: Do not support MMIO to/from encrypted memory
Date: Wed, 28 Oct 2020 12:31:48 -0500 [thread overview]
Message-ID: <a3be983c-a612-51c4-2711-de55c7c68c46@amd.com> (raw)
In-Reply-To: <20201028164659.27002-6-joro@8bytes.org>
On 10/28/20 11:46 AM, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@suse.de>
>
> 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 <jroedel@suse.de>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
> 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;
>
next prev parent reply other threads:[~2020-10-28 22:05 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-28 16:46 [PATCH v4 0/5] x86/sev-es: Mitigate some HV attack vectors Joerg Roedel
2020-10-28 16:46 ` [PATCH v4 1/5] x86/boot/compressed/64: Introduce sev_status Joerg Roedel
2020-10-28 17:14 ` Tom Lendacky
2020-10-29 19:17 ` [tip: x86/seves] " tip-bot2 for Joerg Roedel
2020-10-28 16:46 ` [PATCH v4 2/5] x86/boot/compressed/64: Add CPUID sanity check to early #VC handler Joerg Roedel
2020-10-28 17:15 ` Tom Lendacky
2020-10-29 19:17 ` [tip: x86/seves] x86/boot/compressed/64: Sanity-check CPUID results in the " tip-bot2 for Joerg Roedel
2020-10-28 16:46 ` [PATCH v4 3/5] x86/boot/compressed/64: Check SEV encryption in 64-bit boot-path Joerg Roedel
2020-10-28 17:25 ` Tom Lendacky
2020-10-29 19:17 ` [tip: x86/seves] " tip-bot2 for Joerg Roedel
2020-10-28 16:46 ` [PATCH v4 4/5] x86/head/64: Check SEV encryption before switching to kernel page-table Joerg Roedel
2020-10-28 17:29 ` Tom Lendacky
2020-10-29 19:17 ` [tip: x86/seves] " tip-bot2 for Joerg Roedel
2020-10-28 16:46 ` [PATCH v4 5/5] x86/sev-es: Do not support MMIO to/from encrypted memory Joerg Roedel
2020-10-28 17:31 ` Tom Lendacky [this message]
2020-10-29 19:17 ` [tip: x86/seves] " tip-bot2 for Joerg Roedel
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