Re: [PATCH] efi/arm: fix allocation failure when reserving the kernel base

Ard Biesheuvel
2019-08-19T14:57:10Z

On Mon, 19 Aug 2019 at 11:01, Chester Lin <clin@suse.com> wrote:
>
> Hi Mike and Ard,
>
> On Thu, Aug 15, 2019 at 04:37:39PM +0300, Mike Rapoport wrote:
> > On Thu, Aug 15, 2019 at 02:32:50PM +0300, Ard Biesheuvel wrote:
> > > (adding Mike)
> > >
> > > On Thu, 15 Aug 2019 at 14:28, Chester Lin <clin@suse.com> wrote:
> > > >
> > > > Hi Ard,
> > > >
> > > > On Thu, Aug 15, 2019 at 10:59:43AM +0300, Ard Biesheuvel wrote:
> > > > > On Sun, 4 Aug 2019 at 10:57, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> > > > > >
> > > > > > Hello Chester,
> > > > > >
> > > > > > On Fri, 2 Aug 2019 at 08:40, Chester Lin <clin@suse.com> wrote:
> > > > > > >
> > > > > > > In some cases the arm32 efistub could fail to allocate memory for
> > > > > > > uncompressed kernel. For example, we got the following error message when
> > > > > > > verifying EFI stub on Raspberry Pi-2 [kernel-5.2.1 + grub-2.04] :
> > > > > > >
> > > > > > > EFI stub: Booting Linux Kernel...
> > > > > > > EFI stub: ERROR: Unable to allocate memory for uncompressed kernel.
> > > > > > > EFI stub: ERROR: Failed to relocate kernel
> > > > > > >
> > > > > > > After checking the EFI memory map we found that the first page [0 - 0xfff]
> > > > > > > had been reserved by Raspberry Pi-2's firmware, and the efistub tried to
> > > > > > > set the dram base at 0, which was actually in a reserved region.
> > > > > > >
> > > > > >
> > > > > > This by itself is a violation of the Linux boot protocol for 32-bit
> > > > > > ARM when using the decompressor. The decompressor rounds down its own
> > > > > > base address to a multiple of 128 MB, and assumes the whole area is
> > > > > > available for the decompressed kernel and related data structures.
> > > > > > (The first TEXT_OFFSET bytes are no longer used in practice, which is
> > > > > > why putting a reserved region of 4 KB bytes works at the moment, but
> > > > > > this is fragile). Note that the decompressor does not look at any DT
> > > > > > or EFI provided memory maps *at all*.
> > > > > >
> > > > > > So unfortunately, this is not something we can fix in the kernel, but
> > > > > > we should fix it in the bootloader or in GRUB, so it does not put any
> > > > > > reserved regions in the first 128 MB of memory,
> > > > > >
> > > > >
> > > > > OK, perhaps we can fix this by taking TEXT_OFFSET into account. The
> > > > > ARM boot protocol docs are unclear about whether this memory should be
> > > > > used or not, but it is no longer used for its original purpose (page
> > > > > tables), and the RPi loader already keeps data there.
> > > > >
> > > > > Can you check whether the following patch works for you?
> > > > >
> > > > > diff --git a/drivers/firmware/efi/libstub/Makefile
> > > > > b/drivers/firmware/efi/libstub/Makefile
> > > > > index 0460c7581220..ee0661ddb25b 100644
> > > > > --- a/drivers/firmware/efi/libstub/Makefile
> > > > > +++ b/drivers/firmware/efi/libstub/Makefile
> > > > > @@ -52,6 +52,7 @@ lib-$(CONFIG_EFI_ARMSTUB) += arm-stub.o fdt.o
> > > > > string.o random.o \
> > > > >
> > > > > lib-$(CONFIG_ARM) += arm32-stub.o
> > > > > lib-$(CONFIG_ARM64) += arm64-stub.o
> > > > > +CFLAGS_arm32-stub.o := -DTEXT_OFFSET=$(TEXT_OFFSET)
> > > > > CFLAGS_arm64-stub.o := -DTEXT_OFFSET=$(TEXT_OFFSET)
> > > > >
> > > > > #
> > > > > diff --git a/drivers/firmware/efi/libstub/arm32-stub.c
> > > > > b/drivers/firmware/efi/libstub/arm32-stub.c
> > > > > index e8f7aefb6813..66ff0c8ec269 100644
> > > > > --- a/drivers/firmware/efi/libstub/arm32-stub.c
> > > > > +++ b/drivers/firmware/efi/libstub/arm32-stub.c
> > > > > @@ -204,7 +204,7 @@ efi_status_t
> > > > > handle_kernel_image(efi_system_table_t *sys_table,
> > > > > * loaded. These assumptions are made by the decompressor,
> > > > > * before any memory map is available.
> > > > > */
> > > > > - dram_base = round_up(dram_base, SZ_128M);
> > > > > + dram_base = round_up(dram_base, SZ_128M) + TEXT_OFFSET;
> > > > >
> > > > > status = reserve_kernel_base(sys_table, dram_base, reserve_addr,
> > > > > reserve_size);
> > > > >
> > > >
> > > > I tried your patch on rpi2 and got the following panic. Just a reminder that I
> > > > have replaced some log messages with "......" since it might be too long to
> > > > post all.
> > > >
> > >
> > > OK. Good to know that this change helps you to get past the EFI stub boot issue.
> > >
> > > > In this case the kernel failed to reserve cma, which should hit the issue of
> > > > memblock_limit=0x1000 as I had mentioned in my patch description. The first
> > > > block [0-0xfff] was scanned in adjust_lowmem_bounds(), but it did not align
> > > > with PMD_SIZE so the cma reservation failed because the memblock.current_limit
> > > > was extremely low. That's why I expand the first reservation from 1 PAGESIZE to
> > > > 1 PMD_SIZE in my patch in order to avoid this issue. Please kindly let me know
> > > > if any suggestion, thank you.
> >
> >
> > > This looks like it is a separate issue. The memblock/cma code should
> > > not choke on a reserved page of memory at 0x0.
> > >
> > > Perhaps Russell or Mike (cc'ed) have an idea how to address this?
> >
> > Presuming that the last memblock dump comes from the end of
> > arm_memblock_init() with the this memory map
> >
> > memory[0x0] [0x0000000000000000-0x0000000000000fff], 0x0000000000001000 bytes flags: 0x4
> > memory[0x1] [0x0000000000001000-0x0000000007ef5fff], 0x0000000007ef5000 bytes flags: 0x0
> > memory[0x2] [0x0000000007ef6000-0x0000000007f09fff], 0x0000000000014000 bytes flags: 0x4
> > memory[0x3] [0x0000000007f0a000-0x000000003cb3efff], 0x0000000034c35000 bytes flags: 0x0
> >
> > adjust_lowmem_bounds() will set the memblock_limit (and respectively global
> > memblock.current_limit) to 0x1000 and any further memblock_alloc*() will
> > happily fail.
> >
> > I believe that the assumption for memblock_limit calculations was that the
> > first bank has several megs at least.
> >
> > I wonder if this hack would help:
> >
> > diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> > index d9a0038..948e5b9 100644
> > --- a/arch/arm/mm/mmu.c
> > +++ b/arch/arm/mm/mmu.c
> > @@ -1206,7 +1206,7 @@ void __init adjust_lowmem_bounds(void)
> > * allocated when mapping the start of bank 0, which
> > * occurs before any free memory is mapped.
> > */
> > - if (!memblock_limit) {
> > + if (memblock_limit < PMD_SIZE) {
> > if (!IS_ALIGNED(block_start, PMD_SIZE))
> > memblock_limit = block_start;
> > else if (!IS_ALIGNED(block_end, PMD_SIZE))
> >
>
> I applied this patch as well and it works well on rpi-2 model B.
>

Thanks, Chester, that is good to know.

However, afaict, this only affects systems where physical memory
starts at address 0x0, so I think we need a better fix.

I know Mike has been looking into the NOMAP stuff lately, and your
original patch contains a hunk that makes this code (?) disregard
nomap memblocks. That might be a better approach.