From: Brijesh Singh <brijesh.singh@amd.com>
To: edk2-devel@lists.01.org
Cc: brijesh.singh@amd.com, Tom Lendacky <thomas.lendacky@amd.com>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Laszlo Ersek <lersek@redhat.com>,
Jordan Justen <jordan.l.justen@intel.com>
Subject: Re: [PATCH v1 3/4] OvmfPkg: IommuDxe: Zero the shared page(s) on Unmap()
Date: Mon, 31 Jul 2017 14:38:31 -0500 [thread overview]
Message-ID: <52bcbfac-028e-c4f4-7dac-e0cde14e82f0@amd.com> (raw)
In-Reply-To: <1501529474-20550-4-git-send-email-brijesh.singh@amd.com>
I just realized that this patch contains some changes which should be
part of Patch 2/3. Please ignore this patch for now. I will fix it as part
of v2 when addressing review feedback. thanks
-Brijesh
On 07/31/2017 02:31 PM, Brijesh Singh wrote:
> To support the Map(), we allocate bounce buffer with C-bit cleared,
> the buffer is referred as a DeviceAddress. Typically, DeviceAddress
> is used as communication block between guest and hypervisor. When
> guest is done with communication block, it calls Unmap().The Unmap()
> free's the DeviceAddress, if we do not clear the content of shared
> communication block during Unmap() then data remains readble to the
> hypervisor for an unpredicatable time. Let's zero the bounce buffer
> after we are done using it.
>
> I did some benchmark and did not see any measure perform impact of
> zeroing the page(s).
>
> Suggested-by: Laszlo Ersek <lersek@redhat.com>
> Contributed-under: TianoCore Contribution Agreement 1.0
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
> OvmfPkg/IoMmuDxe/AmdSevIoMmu.c | 18 ++++++++++--------
> 1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/OvmfPkg/IoMmuDxe/AmdSevIoMmu.c b/OvmfPkg/IoMmuDxe/AmdSevIoMmu.c
> index 5ae54482fffe..04e3725ff7e6 100644
> --- a/OvmfPkg/IoMmuDxe/AmdSevIoMmu.c
> +++ b/OvmfPkg/IoMmuDxe/AmdSevIoMmu.c
> @@ -67,8 +67,7 @@ SetBufferAsEncDec (
> // buffer matches with same encryption mask.
> //
> if (!Enc) {
> - Status = MemEncryptSevClearPageEncMask (0, MapInfo->DeviceAddress,
> - MapInfo->NumberOfPages, TRUE);
> + Status = MemEncryptSevClearPageEncMask (0, TempBuffer, MapInfo->NumberOfPages, TRUE);
> ASSERT_EFI_ERROR (Status);
> }
>
> @@ -79,7 +78,7 @@ SetBufferAsEncDec (
> //
> CopyMem (
> (VOID *) (UINTN) TempBuffer,
> - (VOID *) (UINTN)MapInfo->HostAddress,
> + (VOID *) (UINTN) MapInfo->HostAddress,
> MapInfo->NumberOfBytes);
>
> //
> @@ -109,11 +108,8 @@ SetBufferAsEncDec (
> //
> // Restore the encryption mask of the intermediate buffer
> //
> - if (!Enc) {
> - Status = MemEncryptSevSetPageEncMask (0, MapInfo->DeviceAddress,
> - MapInfo->NumberOfPages, TRUE);
> - ASSERT_EFI_ERROR (Status);
> - }
> + Status = MemEncryptSevSetPageEncMask (0, TempBuffer, MapInfo->NumberOfPages, TRUE);
> + ASSERT_EFI_ERROR (Status);
>
> //
> // Free the intermediate buffer
> @@ -386,6 +382,12 @@ IoMmuUnmap (
> ASSERT_EFI_ERROR(Status);
>
> //
> + // Zero the shared memory so that hypervisor no longer able to get intelligentable
> + // data.
> + //
> + SetMem ((VOID *) (UINTN)MapInfo->DeviceAddress, MapInfo->NumberOfBytes, 0);
> +
> + //
> // Free the bounce buffer
> //
> gBS->FreePages (MapInfo->DeviceAddress, MapInfo->NumberOfPages);
>
next prev parent reply other threads:[~2017-07-31 19:36 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-31 19:31 [PATCH v1 0/4] OvmfPkg : IoMmuDxe: BusMasterCommonBuffer support when SEV is active Brijesh Singh
2017-07-31 19:31 ` [PATCH v1 1/4] OvmfPkg: IommuDxe: Do not clear C-bit in Allocate() and Free() Brijesh Singh
2017-08-01 20:42 ` Laszlo Ersek
2017-07-31 19:31 ` [PATCH v1 2/4] OvmfPkg: IommuDxe: Provide support for mapping BusMasterCommonBuffer operation Brijesh Singh
2017-07-31 19:49 ` Ard Biesheuvel
2017-07-31 20:27 ` Brijesh Singh
2017-08-01 20:52 ` Laszlo Ersek
2017-08-01 21:59 ` Laszlo Ersek
2017-08-01 23:51 ` Brijesh Singh
2017-08-02 8:41 ` Laszlo Ersek
2017-07-31 19:31 ` [PATCH v1 3/4] OvmfPkg: IommuDxe: Zero the shared page(s) on Unmap() Brijesh Singh
2017-07-31 19:38 ` Brijesh Singh [this message]
2017-08-02 7:37 ` Laszlo Ersek
2017-08-02 11:22 ` Brijesh Singh
2017-08-02 12:52 ` Laszlo Ersek
2017-07-31 19:31 ` [PATCH v1 4/4] OvmfPkg : QemuFwCfgLib: Map DMA buffer with CommonBuffer when SEV is enable Brijesh Singh
2017-08-02 8:09 ` Laszlo Ersek
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