linux-kernel - Re: [PATCH v4 3/4] efi: Fix efi_memmap

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Message-ID: <CAPcyv4jbf2WR2ZU55564fORxKLf8tGH1XbYBpRfTvPouGWk2mg@mail.gmail.com>
Date:   Mon, 6 Jan 2020 20:24:32 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Dave Young <dyoung@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Taku Izumi <izumi.taku@...fujitsu.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-efi <linux-efi@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kexec Mailing List <kexec@...ts.infradead.org>
Subject: Re: [PATCH v4 3/4] efi: Fix efi_memmap_alloc() leaks

On Mon, Jan 6, 2020 at 7:58 PM Dave Young <dyoung@...hat.com> wrote:
>
> On 01/06/20 at 04:40pm, Dan Williams wrote:
> > With efi_fake_memmap() and efi_arch_mem_reserve() the efi table may be
> > updated and replaced multiple times. When that happens a previous
> > dynamically allocated efi memory map can be garbage collected. Use the
> > new EFI_MEMMAP_{SLAB,MEMBLOCK} flags to detect when a dynamically
> > allocated memory map is being replaced.
> >
> > Debug statements in efi_memmap_free() reveal:
> >
> >  efi: __efi_memmap_free:37: phys: 0x23ffdd580 size: 2688 flags: 0x2
> >  efi: __efi_memmap_free:37: phys: 0x9db00 size: 2640 flags: 0x2
> >  efi: __efi_memmap_free:37: phys: 0x9e580 size: 2640 flags: 0x2
> >
> > ...a savings of 7968 bytes on a qemu boot with 2 entries specified to
> > efi_fake_mem=.
> >
> > Cc: Taku Izumi <izumi.taku@...fujitsu.com>
> > Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> > Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> > ---
> >  drivers/firmware/efi/memmap.c |   24 ++++++++++++++++++++++++
> >  1 file changed, 24 insertions(+)
> >
> > diff --git a/drivers/firmware/efi/memmap.c b/drivers/firmware/efi/memmap.c
> > index 04dfa56b994b..bffa320d2f9a 100644
> > --- a/drivers/firmware/efi/memmap.c
> > +++ b/drivers/firmware/efi/memmap.c
> > @@ -29,6 +29,28 @@ static phys_addr_t __init __efi_memmap_alloc_late(unsigned long size)
> >       return PFN_PHYS(page_to_pfn(p));
> >  }
> >
> > +static void __init __efi_memmap_free(u64 phys, unsigned long size, unsigned long flags)
> > +{
> > +     if (flags & EFI_MEMMAP_MEMBLOCK) {
> > +             if (slab_is_available())
> > +                     memblock_free_late(phys, size);
> > +             else
> > +                     memblock_free(phys, size);
> > +     } else if (flags & EFI_MEMMAP_SLAB) {
> > +             struct page *p = pfn_to_page(PHYS_PFN(phys));
> > +             unsigned int order = get_order(size);
> > +
> > +             free_pages((unsigned long) page_address(p), order);
> > +     }
> > +}
> > +
> > +static void __init efi_memmap_free(void)
> > +{
> > +     __efi_memmap_free(efi.memmap.phys_map,
> > +                     efi.memmap.desc_size * efi.memmap.nr_map,
> > +                     efi.memmap.flags);
> > +}
> > +
> >  /**
> >   * efi_memmap_alloc - Allocate memory for the EFI memory map
> >   * @num_entries: Number of entries in the allocated map.
> > @@ -100,6 +122,8 @@ static int __init __efi_memmap_init(struct efi_memory_map_data *data)
> >               return -ENOMEM;
> >       }
> >
> > +     efi_memmap_free();
> > +
>
> This seems still not safe,  see below function:
> arch/x86/platform/efi/efi.c:
> static void __init efi_clean_memmap(void)
> It use same memmap for both old and new, and filter out those invalid
> ranges in place, if the memory is freed then ..

In the efi_clean_memmap() case flags are 0, so efi_memmap_free() is a nop.

Would you feel better with an explicit?

WARN_ON(efi.memmap.phys_map == data->phys_map && (data->flags &
(EFI_MEMMAP_SLAB | EFI_MEMMAP_MEMBLOCK))

...not sure it's worth it.

>
> >       map.phys_map = data->phys_map;
> >       map.nr_map = data->size / data->desc_size;
> >       map.map_end = map.map + data->size;
> >