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SubjectRe: [PATCH] x86/efi: Map EFI memmap entries in-order at runtime
Hi,

On Wed, Sep 09, 2015 at 12:21:23PM +0100, Matt Fleming wrote:
> On Wed, 09 Sep, at 08:33:07AM, joeyli wrote:
> >
> > Yes, the machine on my hand has EFI_PROPERTIES_TABLE enabled, and it doesn't
> > boot without your patch.
>
> Awesome. Could you test the following patch instead?
>
> ---

Yes, as the first edition, this patch works on my S1200V3RPS machine.

Tested-by: Lee, Chun-Yi <jlee@suse.com>

Regards
Joey Lee

>
> >From 24d324b781a3b688dcc265995949a9cf4e8af687 Mon Sep 17 00:00:00 2001
> From: Matt Fleming <matt.fleming@intel.com>
> Date: Thu, 3 Sep 2015 15:56:25 +0100
> Subject: [PATCH v2] x86/efi: Map EFI memmap entries in-order at runtime
>
> Beginning with UEFI v2.5 EFI_PROPERTIES_TABLE was introduced that
> signals that the firmware PE/COFF loader supports splitting code and
> data sections of PE/COFF images into separate EFI memory map entries.
> This allows the kernel to map those regions with strict memory
> protections, e.g. EFI_MEMORY_RO for code, EFI_MEMORY_XP for data, etc.
>
> Unfortunately, an unwritten requirement of this new feature is that
> the regions need to be mapped with the same offsets relative to each
> other as observed in the EFI memory map. If this is not done crashes
> like this may occur,
>
> [ 0.006391] BUG: unable to handle kernel paging request at fffffffefe6086dd
> [ 0.006923] IP: [<fffffffefe6086dd>] 0xfffffffefe6086dd
> [ 0.007000] Call Trace:
> [ 0.007000] [<ffffffff8104c90e>] efi_call+0x7e/0x100
> [ 0.007000] [<ffffffff81602091>] ? virt_efi_set_variable+0x61/0x90
> [ 0.007000] [<ffffffff8104c583>] efi_delete_dummy_variable+0x63/0x70
> [ 0.007000] [<ffffffff81f4e4aa>] efi_enter_virtual_mode+0x383/0x392
> [ 0.007000] [<ffffffff81f37e1b>] start_kernel+0x38a/0x417
> [ 0.007000] [<ffffffff81f37495>] x86_64_start_reservations+0x2a/0x2c
> [ 0.007000] [<ffffffff81f37582>] x86_64_start_kernel+0xeb/0xef
>
> Here 0xfffffffefe6086dd refers to an address the firmware expects to
> be mapped but which the OS never claimed was mapped. The issue is that
> included in these regions are relative addresses to other regions
> which were emitted by the firmware toolchain before the "splitting" of
> sections occurred at runtime.
>
> Needless to say, we don't satisfy this unwritten requirement on x86_64
> and instead map the EFI memory map entries in reverse order. The above
> crash is almost certainly triggerable with any kernel newer than v3.13
> because that's when we rewrote the EFI runtime region mapping code, in
> commit d2f7cbe7b26a ("x86/efi: Runtime services virtual mapping"). For
> kernel versions before v3.13 things may work by pure luck depending on
> the fragmentation of the kernel virtual address space at the time we
> map the EFI regions.
>
> Instead of mapping the EFI memory map entries in reverse order, where
> entry N has a higher virtual address than entry N+1, map them in the
> same order as they appear in the EFI memory map to preserve this
> relative offset between regions.
>
> This patch has been kept as small as possible with the intention that
> it should be applied aggressively to stable and distribution kernels.
> It is very much a bugfix rather than support for a new feature, since
> when EFI_PROPERTIES_TABLE is enabled we must map things as outlined
> above to even boot - we have no way of asking the firmware not to
> split the code/data regions.
>
> In fact, this patch doesn't even make use of the more strict memory
> protections available in UEFI v2.5. That will come later.
>
> Reported-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Suggested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Lee, Chun-Yi <jlee@suse.com>
> Cc: Borislav Petkov <bp@suse.de>
> Cc: Leif Lindholm <leif.lindholm@linaro.org>
> Cc: Peter Jones <pjones@redhat.com>
> Cc: James Bottomley <JBottomley@Odin.com>
> Cc: Matthew Garrett <mjg59@srcf.ucam.org>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Dave Young <dyoung@redhat.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Matt Fleming <matt.fleming@intel.com>
> ---
>
> v2: Use Ard's reverse iteration scheme so that we can reuse the
> existing efi_map_region() implementation that maps things top-down.
>
> arch/x86/platform/efi/efi.c | 67 ++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 66 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
> index e4308fe6afe8..c6835bfad3a1 100644
> --- a/arch/x86/platform/efi/efi.c
> +++ b/arch/x86/platform/efi/efi.c
> @@ -705,6 +705,70 @@ out:
> }
>
> /*
> + * Iterate the EFI memory map in reverse order because the regions
> + * will be mapped top-down. The end result is the same as if we had
> + * mapped things forward, but doesn't require us to change the
> + * existing implementation of efi_map_region().
> + */
> +static inline void *efi_map_next_entry_reverse(void *entry)
> +{
> + /* Initial call */
> + if (!entry)
> + return memmap.map_end - memmap.desc_size;
> +
> + entry -= memmap.desc_size;
> + if (entry < memmap.map)
> + return NULL;
> +
> + return entry;
> +}
> +
> +/*
> + * efi_map_next_entry - Return the next EFI memory map descriptor
> + * @entry: Previous EFI memory map descriptor
> + *
> + * This is a helper function to iterate over the EFI memory map, which
> + * we do in different orders depending on the current configuration.
> + *
> + * To begin traversing the memory map @entry must be %NULL.
> + *
> + * Returns %NULL when we reach the end of the memory map.
> + */
> +static void *efi_map_next_entry(void *entry)
> +{
> + if (!efi_enabled(EFI_OLD_MEMMAP) && efi_enabled(EFI_64BIT)) {
> + /*
> + * Starting in UEFI v2.5 the EFI_PROPERTIES_TABLE
> + * config table feature requires us to map all entries
> + * in the same order as they appear in the EFI memory
> + * map. That is to say, entry N must have a lower
> + * virtual address than entry N+1. This is because the
> + * firmware toolchain leaves relative references in
> + * the code/data sections, which are split and become
> + * separate EFI memory regions. Mapping things
> + * out-of-order leads to the firmware accessing
> + * unmapped addresses.
> + *
> + * Since we need to map things this way whether or not
> + * the kernel actually makes use of
> + * EFI_PROPERTIES_TABLE, let's just switch to this
> + * scheme by default for 64-bit.
> + */
> + return efi_map_next_entry_reverse(entry);
> + }
> +
> + /* Initial call */
> + if (!entry)
> + return memmap.map;
> +
> + entry += memmap.desc_size;
> + if (entry >= memmap.map_end)
> + return NULL;
> +
> + return entry;
> +}
> +
> +/*
> * Map the efi memory ranges of the runtime services and update new_mmap with
> * virtual addresses.
> */
> @@ -714,7 +778,8 @@ static void * __init efi_map_regions(int *count, int *pg_shift)
> unsigned long left = 0;
> efi_memory_desc_t *md;
>
> - for (p = memmap.map; p < memmap.map_end; p += memmap.desc_size) {
> + p = NULL;
> + while ((p = efi_map_next_entry(p))) {
> md = p;
> if (!(md->attribute & EFI_MEMORY_RUNTIME)) {
> #ifdef CONFIG_X86_64
> --
> 2.1.0
>
> --
> Matt Fleming, Intel Open Source Technology Center


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