[edk2-devel] [PATCH RFC v2 05/28] MdePkg: Add AsmPvalidate() support
Laszlo Ersek
lersek at redhat.com
Tue May 4 13:58:26 UTC 2021
On 04/30/21 13:51, Brijesh Singh wrote:
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3275
>
> The PVALIDATE instruction validates or rescinds validation of a guest
> page RMP entry. Upon completion, a return code is stored in EAX, rFLAGS
> bits OF, ZF, AF, PF and SF are set based on this return code. If the
> instruction completed succesfully, the rFLAGS bit CF indicates if the
> contents of the RMP entry were changed or not.
>
> For more information about the instruction see AMD APM volume 3.
>
> Cc: James Bottomley <jejb at linux.ibm.com>
> Cc: Min Xu <min.m.xu at intel.com>
> Cc: Jiewen Yao <jiewen.yao at intel.com>
> Cc: Tom Lendacky <thomas.lendacky at amd.com>
> Cc: Jordan Justen <jordan.l.justen at intel.com>
> Cc: Ard Biesheuvel <ardb+tianocore at kernel.org>
> Cc: Laszlo Ersek <lersek at redhat.com>
> Cc: Erdem Aktas <erdemaktas at google.com>
> Signed-off-by: Brijesh Singh <brijesh.singh at amd.com>
> ---
> MdePkg/Include/Library/BaseLib.h | 37 +++++++++++++++++
> MdePkg/Library/BaseLib/BaseLib.inf | 1 +
> MdePkg/Library/BaseLib/X64/Pvalidate.nasm | 43 ++++++++++++++++++++
> 3 files changed, 81 insertions(+)
>
> diff --git a/MdePkg/Include/Library/BaseLib.h b/MdePkg/Include/Library/BaseLib.h
> index 7253997a6f..92ce695e93 100644
> --- a/MdePkg/Include/Library/BaseLib.h
> +++ b/MdePkg/Include/Library/BaseLib.h
> @@ -7518,5 +7518,42 @@ PatchInstructionX86 (
> IN UINTN ValueSize
> );
>
> +/**
> + Execute a PVALIDATE instruction to validate or rescnids validation of a guest
(1) typo: "rescnids"
> + page's RMP entry.
> +
> + Upon completion, in addition to the return value the instruction also updates
> + the eFlags. A caller must check both the return code as well as eFlags to
> + determine if the RMP entry has been updated.
> +
> + The function is available on x64.
(2) Please write "X64"; that's how the architecture is usually mentioned
in both the UEFI spec and in edk2.
> +
> + @param[in] Address The guest virtual address to validate.
> + @param[in] PageSize The page size to use.
> + @param[i] Validate Validate or rescinds.
> + @param[out] Eflags The value of Eflags after PVALIDATE completion.
(3) Typo: "[i]" should be "[in]".
(4) The order of parameters listed in this comment block differs from
the actual parameter list.
The ECC plugin of the edk2 CI will catch this issue anyway. So, before
submitting the patch set to the list, please submit a personal PR on
github.com against the main repo, just to run CI on your patches.
> +
> + @retval PvalidateRetValue The return value from the PVALIDATE instruction.
More on the return value / type later, below.
> +**/
> +typedef enum {
> + PvalidatePageSize4K = 0,
> + PvalidatePageSize2MB,
> +} PVALIDATE_PAGE_SIZE;
> +
> +typedef enum {
> + PvalidateRetSuccess = 0,
> + PvalidateRetFailInput = 1,
> + PvalidateRetFailSizemismatch = 6,
> +} PVALIDATE_RET_VALUE;
> +
(5) These typedefs do not belong between the function leading comment
and the function declaration. Please hoist the typedefs just above the
leading comment, and add a separate comment for the typedefs -- using
the proper comment style for typedefs, too.
> +PVALIDATE_RET_VALUE
(6) In my opinion, using an enum for an EFIAPI function's return type is
problematic. According to the UEFI spec (v2.9), "Table 2-3 Common UEFI
Data Types", <Enumerated Type> may correspond to INT32 or UINT32. I
don't like that ambiguity here. The spec also says that such types
should never be used at least as structure fields.
I'm perfectly fine with functions in standard (ISO) C programs returning
enums, but I think the situation is less clear in UEFI. I don't recall
standard interfaces (spec-level, or even edk2 / MdePkg interfaces) that
return enums.
I suggest the following instead. Drop the PVALIDATE_RET_VALUE enum
altogether. Specify EFI_STATUS as the return type, in the declaration of
the function.
In the UEFI spec, Appendix D specifies the numeric values of the status
codes. Furthermore, there are examples for NASM sources using EFI_*
status codes *numerically* in edk2; minimally:
- IntelFsp2Pkg/FspSecCore/Ia32/FspApiEntryT.nasm
- IntelFsp2WrapperPkg/Library/SecFspWrapperPlatformSecLibSample/Ia32/SecEntry.nasm
Thus, please modify the assembly source code in this patch to return
EFI_SUCCESS (already value 0, conveniently) if the instruction succeeds.
Return EFI_INVALID_PARAMETER (0x8000_0002) in case the instruction fails
with error code 1 (FAIL_INPUT).
Return EFI_UNSUPPORTED (0x8000_0003), or even EFI_NO_MAPPING
(0x8000_0017), for value 6 (FAIL_SIZEMISMATCH).
The leading comment block of the function is supposed to explain these
associations:
@retval EFI_SUCCESS Successful completion (regardless of
whether the Validated bit changed state).
@retval INVALID_PARAMETER Invalid input parameters (FAIL_INPUT).
@retval EFI_UNSUPPORTED Page size mismatch between guest (2M) and
RMP entry (4K) (FAIL_SIZEMISMATCH).
(Passing in the PVALIDATE_PAGE_SIZE enum, as a parameter, should be
fine, BTW)
(7) According to the AMD APM, "Support for this instruction is indicated
by CPUID Fn8000_001F_EAX[SNP]=1".
Presumably, if the (physical, or emulated) hardware does not support
PVALIDATE, an #UD is raised. That condition should be explained in the
function's leading comment. (Mention the CPUID and the #UD, I guess.)
> +EFIAPI
> +AsmPvalidate (
> + IN PVALIDATE_PAGE_SIZE PageSize,
> + IN BOOLEAN Validate,
> + IN UINTN Address,
(8) This should be EFI_PHYSICAL_ADDRESS, not UINTN.
> + OUT IA32_EFLAGS32 *Eflags
> + );
> +
> #endif // defined (MDE_CPU_IA32) || defined (MDE_CPU_X64)
> #endif // !defined (__BASE_LIB__)
(9) Unless you foresee particular uses for eflags *other than* CF, I
would suggest replacing the Eflags output parameter with
OUT BOOLEAN *RmpEntryUpdated
The function would still only have 4 parameters, which shouldn't be
difficult to handle in the assembly implementation (i.e. write to the
UINT8 (= BOOLEAN) object referenced by "RmpEntryUpdated"). EFIAPI means
that the first four params are passed in RCX, RDX, R8, R9.
Thus far, I can see only one AsmPvalidate() call: in IssuePvalidate(),
from patch #21 ("OvmfPkg/MemEncryptSevLib: Add support to validate
system RAM"). And there, CF looks sufficient.
(10) The instruction is X64 only, but you are providing the declaration
even if MDE_CPU_IA32 is #defined. That seems wrong; even the declaration
should be invisible in that case. Please declare the function for
MDE_CPU_X64 only.
> diff --git a/MdePkg/Library/BaseLib/BaseLib.inf b/MdePkg/Library/BaseLib/BaseLib.inf
> index b76f3af380..d33b4a8f7d 100644
> --- a/MdePkg/Library/BaseLib/BaseLib.inf
> +++ b/MdePkg/Library/BaseLib/BaseLib.inf
> @@ -321,6 +321,7 @@
> X64/XGetBv.nasm
> X64/XSetBv.nasm
> X64/VmgExit.nasm
> + X64/Pvalidate.nasm
> ChkStkGcc.c | GCC
>
> [Sources.EBC]
(11) This list of source files is already not sorted alphabetically,
unfortunately. But we can still do better than this: I suggest inserting
"X64/Pvalidate.nasm" just before "X64/RdRand.nasm".
(12) Your git setup seems less than ideal for formatting edk2 patches.
The @@ hunk header above does not show the INF file section being
modified. It should look something like this:
@@ -317,6 +317,7 @@ [Sources.X64]
^^^^^^^^^^^^^
Please run the "BaseTools/Scripts/SetupGit.py" script in your working
tree.
Alternatively, please see "xfuncname" at
<https://github.com/tianocore/tianocore.github.io/wiki/Laszlo%27s-unkempt-git-guide-for-edk2-contributors-and-maintainers#contrib-05>.
This is of course not a bug in the patch, but fixing your setup will
help with the next round of review.
> diff --git a/MdePkg/Library/BaseLib/X64/Pvalidate.nasm b/MdePkg/Library/BaseLib/X64/Pvalidate.nasm
> new file mode 100644
> index 0000000000..f2aba114ac
> --- /dev/null
> +++ b/MdePkg/Library/BaseLib/X64/Pvalidate.nasm
> @@ -0,0 +1,43 @@
> +;-----------------------------------------------------------------------------
> +;
> +; Copyright (c) 2020-2021, AMD. All rights reserved.<BR>
(13) I believe we don't introduce new files with copyright notices
referring to the past. IOW, I think you should only say "2021" here.
> +; SPDX-License-Identifier: BSD-2-Clause-Patent
> +;
> +; Module Name:
> +;
> +; Pvalidate.Asm
> +;
> +; Abstract:
> +;
> +; AsmPvalidate function
> +;
> +; Notes:
> +;
(14) I defer to the MdePkg maintainers on this, but "Module Name" is
plain wrong, and the Abstract is useless. Either fix those up please
("Abstract" could be a copy of the corrected leading comment block), or
just drop them both.
> +;-----------------------------------------------------------------------------
> +
> + SECTION .text
> +
> +;-----------------------------------------------------------------------------
> +; PvalidateRetValue
> +; EFIAPI
> +; AsmPvalidate (
> +; IN UINT32 RmpPageSize
> +; IN UINT32 Validate,
> +; IN UINTN Address,
> +; OUT UINTN *Eflags,
> +; )
> +;-----------------------------------------------------------------------------
(15) Please update this accordingly to the corrected function
specification.
> +global ASM_PFX(AsmPvalidate)
> +ASM_PFX(AsmPvalidate):
> + mov rax, r8
> +
> + ; PVALIDATE instruction opcode
> + DB 0xF2, 0x0F, 0x01, 0xFF
This is bad practice; we make every effort to avoid DB-encoded
instructions.
We have two PVALIDATE instances in the patch set (... that I can see
immediateyl); the first here, and the other in
"OvmfPkg/ResetVector/Ia32/PageTables64.asm" (from patch #17,
"OvmfPkg/ResetVector: Invalidate the GHCB page"). Therefore, hiding the
encoding of PVALIDATE behind a NASM macro definitely makes sense.
(16a) Please file a NASM feature request for PVALIDATE at
<https://bugzilla.nasm.us>.
(16b) In the present MdePkg patch, please extend the file
MdePkg/Include/X64/Nasm.inc
as follows:
> diff --git a/MdePkg/Include/X64/Nasm.inc b/MdePkg/Include/X64/Nasm.inc
> index 527f71e9eb4d..ff37f1e35707 100644
> --- a/MdePkg/Include/X64/Nasm.inc
> +++ b/MdePkg/Include/X64/Nasm.inc
> @@ -33,6 +33,15 @@
> DB 0xF3, 0x48, 0x0F, 0xAE, 0xE8
> %endmacro
>
> +;
> +; Macro for the PVALIDATE instruction, defined in AMD publication #24594
> +; revision 3.32. NASM feature request URL:
> +; <https://bugzilla.nasm.us/show_bug.cgi?id=FIXME>.
> +;
> +%macro PVALIDATE 0
> + DB 0xF2, 0x0F, 0x01, 0xFF
> +%endmacro
> +
> ; NASM provides built-in macros STRUC and ENDSTRUC for structure definition.
> ; For example, to define a structure called mytype containing a longword,
> ; a word, a byte and a string of bytes, you might code
(16c) Please replace the FIXME placeholder above with the actual NASM BZ
number (from (16a)).
(16d) In the "MdePkg/Library/BaseLib/X64/Pvalidate.nasm" source file,
and also (later) in the "OvmfPkg/ResetVector/Ia32/PageTables64.asm"
source file, please use the PVALIDATE macro, in place of the naked DBs.
Back to your patch:
On 04/30/21 13:51, Brijesh Singh wrote:
> +
> + ; Read the Eflags
> + pushfq
> + pop r8
> + mov [r9], r8
> +
> + ; The PVALIDATE instruction returns the status in rax register.
> + ret
>
(17) The assembly code should be updated to match the new interface
contract (parameter order, parameter types, return values).
I'll continue reviewing the series later this week (hopefully tomorrow).
Thanks,
Laszlo
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