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From: Ard Biesheuvel <ardb@kernel.org>
To: Tom Lendacky <thomas.lendacky@amd.com>
Cc: linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
	Evgeniy Baskov <baskov@ispras.ru>, Borislav Petkov <bp@alien8.de>,
	Andy Lutomirski <luto@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Alexey Khoroshilov <khoroshilov@ispras.ru>,
	Peter Jones <pjones@redhat.com>,
	Gerd Hoffmann <kraxel@redhat.com>, Dave Young <dyoung@redhat.com>,
	Mario Limonciello <mario.limonciello@amd.com>,
	Kees Cook <keescook@chromium.org>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH v2 18/20] x86: efistub: Avoid legacy decompressor when doing EFI boot
Date: Fri, 19 May 2023 00:33:20 +0200	[thread overview]
Message-ID: <CAMj1kXFvfyPibZWTLUaLb6pJQWJbV2p7wV__dcCAyjLAuPrtQg@mail.gmail.com> (raw)
In-Reply-To: <a7580b4c-09f3-da32-8547-5b0193709c16@amd.com>

On Thu, 18 May 2023 at 22:48, Tom Lendacky <thomas.lendacky@amd.com> wrote:
>
> On 5/8/23 02:03, Ard Biesheuvel wrote:
> > The bare metal decompressor code was never really intended to run in a
> > hosted environment such as the EFI boot services, and does a few things
> > that are problematic in the context of EFI boot now that the logo
> > requirements are getting tighter.
> >
> > In particular, the decompressor moves its own executable image around in
> > memory, and relies on demand paging to populate the identity mappings,
> > and these things are difficult to support in a context where memory is
> > not permitted to be mapped writable and executable at the same time or,
> > at the very least, is mapped non-executable by default, and needs
> > special treatment for this restriction to be lifted.
> >
> > Since EFI already maps all of memory 1:1, we don't need to create new
> > page tables or handle page faults when decompressing the kernel. That
> > means there is also no need to replace the special exception handlers
> > for SEV. Generally, there is little need to do anything that the
> > decompressor does beyond
> >
> > - initialize SEV encryption, if needed,
> > - perform the 4/5 level paging switch, if needed,
> > - decompress the kernel
> > - relocate the kernel
> >
> > So let's do all of this from the EFI stub code, and avoid the bare metal
> > decompressor altogether.
>
> This patch crashes SEV guests, probably because of the BSS is accessed
> encrypted and results in ciphertext for what would be a zero for a non-SEV
> guest. After pushing patch #19 everything started working again. From a
> bisectability perspective, you probably want patch #19 before this one.
>

Noted, thanks.

  reply	other threads:[~2023-05-18 22:33 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-05-08  7:03 [PATCH v2 00/20] efi/x86: Avoid bare metal decompressor during EFI boot Ard Biesheuvel
2023-05-08  7:03 ` [PATCH v2 01/20] x86: decompressor: Use proper sequence to take the address of the GOT Ard Biesheuvel
2023-05-17 17:31   ` Borislav Petkov
2023-05-17 17:39     ` Ard Biesheuvel
2023-05-08  7:03 ` [PATCH v2 02/20] x86: decompressor: Store boot_params pointer in callee save register Ard Biesheuvel
2023-05-08  7:03 ` [PATCH v2 03/20] x86: decompressor: Call trampoline as a normal function Ard Biesheuvel
2023-05-15 13:59   ` Kirill A. Shutemov
2023-05-08  7:03 ` [PATCH v2 04/20] x86: decompressor: Use standard calling convention for trampoline Ard Biesheuvel
2023-05-15 14:00   ` Kirill A. Shutemov
2023-05-08  7:03 ` [PATCH v2 05/20] x86: decompressor: Avoid the need for a stack in the 32-bit trampoline Ard Biesheuvel
2023-05-15 14:03   ` Kirill A. Shutemov
2023-05-17 22:40   ` Tom Lendacky
2023-05-18 14:55     ` Ard Biesheuvel
2023-05-08  7:03 ` [PATCH v2 06/20] x86: decompressor: Call trampoline directly from C code Ard Biesheuvel
2023-05-15 14:05   ` Kirill A. Shutemov
2023-05-08  7:03 ` [PATCH v2 07/20] x86: decompressor: Only call the trampoline when changing paging levels Ard Biesheuvel
2023-05-15 14:07   ` Kirill A. Shutemov
2023-05-08  7:03 ` [PATCH v2 08/20] x86: decompressor: Merge trampoline cleanup with switching code Ard Biesheuvel
     [not found]   ` <20230515140955.d4adbstv6gtnshp2@box.shutemov.name>
2023-05-16 17:50     ` Ard Biesheuvel
2023-05-08  7:03 ` [PATCH v2 09/20] x86: efistub: Perform 4/5 level paging switch from the stub Ard Biesheuvel
2023-05-15 14:14   ` Kirill A. Shutemov
2023-05-16 17:53     ` Ard Biesheuvel
2023-05-08  7:03 ` [PATCH v2 10/20] x86: efistub: Prefer EFI memory attributes protocol over DXE services Ard Biesheuvel
2023-05-08  7:03 ` [PATCH v2 11/20] decompress: Use 8 byte alignment Ard Biesheuvel
2023-05-08  7:03 ` [PATCH v2 12/20] x86: decompressor: Move global symbol references to C code Ard Biesheuvel
2023-05-08  7:03 ` [PATCH v2 13/20] x86: decompressor: Factor out kernel decompression and relocation Ard Biesheuvel
2023-05-08  7:03 ` [PATCH v2 14/20] x86: head_64: Store boot_params pointer in callee-preserved register Ard Biesheuvel
2023-05-08  7:03 ` [PATCH v2 15/20] x86: head_64: Switch to kernel CS before enabling memory encryption Ard Biesheuvel
2023-05-17 18:54   ` Tom Lendacky
2023-05-08  7:03 ` [PATCH v2 16/20] efi: libstub: Add limit argument to efi_random_alloc() Ard Biesheuvel
2023-05-08  7:03 ` [PATCH v2 17/20] x86: efistub: Check SEV/SNP support while running in the firmware Ard Biesheuvel
2023-05-18 20:16   ` Tom Lendacky
2023-05-18 22:27     ` Ard Biesheuvel
2023-05-19 14:04       ` Tom Lendacky
2023-05-22 12:48         ` Joerg Roedel
2023-05-22 13:07           ` Ard Biesheuvel
2023-05-22 13:35             ` Joerg Roedel
2023-05-08  7:03 ` [PATCH v2 18/20] x86: efistub: Avoid legacy decompressor when doing EFI boot Ard Biesheuvel
2023-05-18 20:48   ` Tom Lendacky
2023-05-18 22:33     ` Ard Biesheuvel [this message]
2023-05-08  7:03 ` [PATCH v2 19/20] x86: efistub: Clear BSS in EFI handover protocol entrypoint Ard Biesheuvel
2023-05-08  7:03 ` [PATCH v2 20/20] x86: decompressor: Avoid magic offsets for EFI handover entrypoint Ard Biesheuvel

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