Re: [PATCH AUTOSEL 4.19 17/49] efi/x86/Add missing error handling to old_memmap 1:1 mapping code

On Sat, 8 Jun 2019 at 13:43, Sasha Levin sashal@kernel.org wrote:

From: Gen Zhang blackgod016574@gmail.com

[ Upstream commit 4e78921ba4dd0aca1cc89168f45039add4183f8e ]

The old_memmap flow in efi_call_phys_prolog() performs numerous memory allocations, and either does not check for failure at all, or it does but fails to propagate it back to the caller, which may end up calling into the firmware with an incomplete 1:1 mapping.

So let's fix this by returning NULL from efi_call_phys_prolog() on memory allocation failures only, and by handling this condition in the caller. Also, clean up any half baked sets of page tables that we may have created before returning with a NULL return value.

Note that any failure at this level will trigger a panic() two levels up, so none of this makes a huge difference, but it is a nice cleanup nonetheless.

[ardb: update commit log, add efi_call_phys_epilog() call on error path]

Signed-off-by: Gen Zhang blackgod016574@gmail.com Signed-off-by: Ard Biesheuvel ard.biesheuvel@linaro.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Rob Bradford robert.bradford@intel.com Cc: Thomas Gleixner tglx@linutronix.de Cc: linux-efi@vger.kernel.org Link: http://lkml.kernel.org/r/20190525112559.7917-2-ard.biesheuvel@linaro.org Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org

This was already discussed in the thread that proposed this patch for stable: please don't queue this right now, the patches are more likely to harm than hurt, and they certainly don't fix a security vulnerability, as has been claimed.

---

arch/x86/platform/efi/efi.c | 2 ++ arch/x86/platform/efi/efi_64.c | 9 ++++++--- 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c index 9061babfbc83..353019d4e6c9 100644 --- a/arch/x86/platform/efi/efi.c +++ b/arch/x86/platform/efi/efi.c @@ -86,6 +86,8 @@ static efi_status_t __init phys_efi_set_virtual_address_map( pgd_t *save_pgd;

    save_pgd = efi_call_phys_prolog();

•   if (!save_pgd)
  

•           return EFI_ABORTED;
  
    /* Disable interrupts around EFI calls: */
    local_irq_save(flags);
  

diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c index ee5d08f25ce4..dfc809b31c7c 100644 --- a/arch/x86/platform/efi/efi_64.c +++ b/arch/x86/platform/efi/efi_64.c @@ -84,13 +84,15 @@ pgd_t * __init efi_call_phys_prolog(void)

    if (!efi_enabled(EFI_OLD_MEMMAP)) {
            efi_switch_mm(&efi_mm);

•           return NULL;
  

•           return efi_mm.pgd;
    }
  
    early_code_mapping_set_exec(1);
  
    n_pgds = DIV_ROUND_UP((max_pfn << PAGE_SHIFT), PGDIR_SIZE);
    save_pgd = kmalloc_array(n_pgds, sizeof(*save_pgd), GFP_KERNEL);
  

•   if (!save_pgd)
  

•           return NULL;
  
    /*
     * Build 1:1 identity mapping for efi=old_map usage. Note that
  

@@ -138,10 +140,11 @@ pgd_t * __init efi_call_phys_prolog(void) pgd_offset_k(pgd * PGDIR_SIZE)->pgd &= ~_PAGE_NX; }

-out: __flush_tlb_all();

•   return save_pgd;
  

+out:

•   efi_call_phys_epilog(save_pgd);
  

•   return NULL;
  

}

void __init efi_call_phys_epilog(pgd_t *save_pgd)

2.20.1