linux-kernel - Re: [PATCH v4 07/11] efi/libstub: Add generic support for parsing mem

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Date: Tue, 20 Feb 2024 13:28:00 -0600
From: Tom Lendacky <thomas.lendacky@....com>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Ard Biesheuvel <ardb+git@...gle.com>, linux-kernel@...r.kernel.org,
 Kevin Loughlin <kevinloughlin@...gle.com>,
 Dionna Glaze <dionnaglaze@...gle.com>, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>, Andy Lutomirski
 <luto@...nel.org>, Arnd Bergmann <arnd@...db.de>,
 Nathan Chancellor <nathan@...nel.org>,
 Nick Desaulniers <ndesaulniers@...gle.com>,
 Justin Stitt <justinstitt@...gle.com>, Kees Cook <keescook@...omium.org>,
 Brian Gerst <brgerst@...il.com>, linux-arch@...r.kernel.org,
 llvm@...ts.linux.dev
Subject: Re: [PATCH v4 07/11] efi/libstub: Add generic support for parsing
 mem_encrypt=

On 2/19/24 11:06, Ard Biesheuvel wrote:
> On Mon, 19 Feb 2024 at 18:00, Tom Lendacky <thomas.lendacky@....com> wrote:
>>
>> On 2/13/24 06:41, Ard Biesheuvel wrote:
>>> From: Ard Biesheuvel <ardb@...nel.org>
>>>
>>> Parse the mem_encrypt= command line parameter from the EFI stub if
>>> CONFIG_ARCH_HAS_MEM_ENCRYPT=y, so that it can be passed to the early
>>> boot code by the arch code in the stub.
>>>
>>> This avoids the need for the core kernel to do any string parsing very
>>> early in the boot.
>>>
>>> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
>>> ---
>>>    drivers/firmware/efi/libstub/efi-stub-helper.c | 8 ++++++++
>>>    drivers/firmware/efi/libstub/efistub.h         | 2 +-
>>>    2 files changed, 9 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
>>> index bfa30625f5d0..3dc2f9aaf08d 100644
>>> --- a/drivers/firmware/efi/libstub/efi-stub-helper.c
>>> +++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
>>> @@ -24,6 +24,8 @@ static bool efi_noinitrd;
>>>    static bool efi_nosoftreserve;
>>>    static bool efi_disable_pci_dma = IS_ENABLED(CONFIG_EFI_DISABLE_PCI_DMA);
>>>
>>> +int efi_mem_encrypt;
>>> +
>>>    bool __pure __efi_soft_reserve_enabled(void)
>>>    {
>>>        return !efi_nosoftreserve;
>>> @@ -75,6 +77,12 @@ efi_status_t efi_parse_options(char const *cmdline)
>>>                        efi_noinitrd = true;
>>>                } else if (IS_ENABLED(CONFIG_X86_64) && !strcmp(param, "no5lvl")) {
>>>                        efi_no5lvl = true;
>>> +             } else if (IS_ENABLED(CONFIG_ARCH_HAS_MEM_ENCRYPT) &&
>>> +                        !strcmp(param, "mem_encrypt") && val) {
>>> +                     if (parse_option_str(val, "on"))
>>> +                             efi_mem_encrypt = 1;
>>> +                     else if (parse_option_str(val, "off"))
>>> +                             efi_mem_encrypt = -1;
>>
>> With CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT having recently been
>> removed, I'm not sure what parsing for mem_encrypt=off does.
>>
>> (Same thing in the next patch.)
>>
> 
> We have to deal with both mem_encrypt=on and mem_encrypt=off occurring
> on the command line. efi_parse_options() may be called more than once,
> i.e., when there is a default command line baked into the image that
> can be overridden at runtime. So if the baked in one has
> mem_encrypt=on, mem_encrypt=off appearing later should counter that.
> 
> The same applies to the next patch, although the decompressor appears
> to ignore the built-in command line entirely (I made a note of that in
> the commit log)

Ah, makes sense.

Thanks,
Tom