linux-kernel - Re: [RFCv2 1/9] efi/libstub: Ask efi_random

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Message-ID: <CAMj1kXG_TynaQni6mzXYg6sCybSMba7cuwnyb4qi5LNZ=53pKQ@mail.gmail.com>
Date: Wed, 28 Aug 2024 15:28:01 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Pingfan Liu <piliu@...hat.com>
Cc: linux-efi@...r.kernel.org, Jan Hendrik Farr <kernel@...rr.cc>, 
	Philipp Rudo <prudo@...hat.com>, Lennart Poettering <mzxreary@...inter.de>, 
	Jarkko Sakkinen <jarkko@...nel.org>, Eric Biederman <ebiederm@...ssion.com>, Baoquan He <bhe@...hat.com>, 
	Dave Young <dyoung@...hat.com>, Mark Rutland <mark.rutland@....com>, Will Deacon <will@...nel.org>, 
	Catalin Marinas <catalin.marinas@....com>, kexec@...ts.infradead.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [RFCv2 1/9] efi/libstub: Ask efi_random_alloc() to skip unusable memory

On Mon, 19 Aug 2024 at 16:55, Pingfan Liu <piliu@...hat.com> wrote:
>
> efi_random_alloc() demands EFI_ALLOCATE_ADDRESS when allocate_pages(),
> but the current implement can not ensure the selected target locates
> inside free area, that is to exclude EFI_BOOT_SERVICES_*,
> EFI_RUNTIME_SERVICES_* etc.
>
> Fix the issue by checking md->type.
>
> Signed-off-by: Pingfan Liu <piliu@...hat.com>
> Cc: Ard Biesheuvel <ardb@...nel.org>
> To: linux-efi@...r.kernel.org
> ---
>  drivers/firmware/efi/libstub/randomalloc.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/drivers/firmware/efi/libstub/randomalloc.c b/drivers/firmware/efi/libstub/randomalloc.c
> index c41e7b2091cdd..7304e767688f2 100644
> --- a/drivers/firmware/efi/libstub/randomalloc.c
> +++ b/drivers/firmware/efi/libstub/randomalloc.c
> @@ -79,6 +79,8 @@ efi_status_t efi_random_alloc(unsigned long size,
>                 efi_memory_desc_t *md = (void *)map->map + map_offset;
>                 unsigned long slots;
>
> +               if (!(md->type & (EFI_CONVENTIONAL_MEMORY || EFI_PERSISTENT_MEMORY)))
> +                       continue;

This is wrong in 3 different ways:
- md->type is not a bitmask
- || is not bitwise but boolean
- get_entry_num_slots() ignores all memory types except
EFI_CONVENTIONAL_MEMORY anyway.

So what exactly are you trying to fix here?


>                 slots = get_entry_num_slots(md, size, ilog2(align), alloc_min,
>                                             alloc_max);
>                 MD_NUM_SLOTS(md) = slots;
> @@ -111,6 +113,9 @@ efi_status_t efi_random_alloc(unsigned long size,
>                 efi_physical_addr_t target;
>                 unsigned long pages;
>
> +               if (!(md->type & (EFI_CONVENTIONAL_MEMORY || EFI_PERSISTENT_MEMORY)))
> +                       continue;
> +
>                 if (total_mirrored_slots > 0 &&
>                     !(md->attribute & EFI_MEMORY_MORE_RELIABLE))
>                         continue;
> --
> 2.41.0
>