Re: [PATCH] x86/efi: Add necessary checks before iterating over efi.memmap

[Chao Gao <chao.gao-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>]

On Tue, Sep 13, 2016 at 09:51:39AM +0100, Ard Biesheuvel wrote:
>On 13 September 2016 at 04:28, Chao Gao <chao.gao-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> wrote:
>> Commit 78ce248f (efi: Iterate over efi.memmap in for_each_efi_memory_desc())
>> replaces the old loop by for_each_efi_memory_desc() which will encounter #PF
>> when efi.memap are not initialized.
>>
>> In boot process, xen set EFI_PARAVIRT in xen_efi_init() before setup_arch()
>> is called. This leads efi_memmap_init() will not initialize structures
>> related to efi.memmap. However, the following functions e.g.
>> efi_find_mirror(), efi_print_memmap() and efi_free_boot_services() access
>> efi.memmap without necessary checks. kernel and xen crash in this case.
>> After adding these checks, xen and kernel boot up normally.
>>
>
>OK, so looking at the hunks below, it looks to me like we should
>initialize the efi.memmap to sane values in the EFI_PARAVIRT case,
>rather than open coding this test each time for_each_efi_memory_desc()
>is invoked.
>

Ard, thanks for you reply.
Yes, I think what you say is also a solution. This patch just uses the same method
using by some existed functions such as efi_memblock_x86_reserve_range() and 
efi_runtime_init(). we can handle cases with existed flags correctly and the checks
seems not too much. Maybe we can try what you say when it's really needed.

>> Signed-off-by: Chao Gao <chao.gao-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
>> ---
>>  arch/x86/platform/efi/efi.c    | 6 ++++++
>>  arch/x86/platform/efi/quirks.c | 3 +++
>>  2 files changed, 9 insertions(+)
>>
>> diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
>> index 1fbb408..68966dc 100644
>> --- a/arch/x86/platform/efi/efi.c
>> +++ b/arch/x86/platform/efi/efi.c
>> @@ -102,6 +102,9 @@ void __init efi_find_mirror(void)
>>         efi_memory_desc_t *md;
>>         u64 mirror_size = 0, total_size = 0;
>>
>> +       if (efi_enabled(EFI_PARAVIRT))
>> +               return;
>> +
>>         for_each_efi_memory_desc(md) {
>>                 unsigned long long start = md->phys_addr;
>>                 unsigned long long size = md->num_pages << EFI_PAGE_SHIFT;
>> @@ -207,6 +210,9 @@ void __init efi_print_memmap(void)
>>         efi_memory_desc_t *md;
>>         int i = 0;
>>
>> +       if (efi_enabled(EFI_PARAVIRT))
>> +               return;
>> +
>>         for_each_efi_memory_desc(md) {
>>                 char buf[64];
>>
>> diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
>> index 89d1146..4fa1e4d 100644
>> --- a/arch/x86/platform/efi/quirks.c
>> +++ b/arch/x86/platform/efi/quirks.c
>> @@ -251,6 +251,9 @@ void __init efi_free_boot_services(void)
>>  {
>>         efi_memory_desc_t *md;
>>
>> +       if (efi_enabled(EFI_PARAVIRT))
>> +               return;
>> +
>>         for_each_efi_memory_desc(md) {
>>                 unsigned long long start = md->phys_addr;
>>                 unsigned long long size = md->num_pages << EFI_PAGE_SHIFT;
>> --
>> 1.8.3.1
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-efi" in
>> the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html