ACK/Cmnt: [PATCH Disco/master] efi/x86/Add missing error handling to old_memmap 1:1 mapping code

[Stefan Bader]

On 08.06.20 20:50, Benjamin M Romer wrote:
> From: Gen Zhang <blackgod016574 at gmail.com>
> 
> 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 at gmail.com>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> Cc: Linus Torvalds <torvalds at linux-foundation.org>
> Cc: Peter Zijlstra <peterz at infradead.org>
> Cc: Rob Bradford <robert.bradford at intel.com>
> Cc: Thomas Gleixner <tglx at linutronix.de>
> Cc: linux-efi at vger.kernel.org
> Link: http://lkml.kernel.org/r/20190525112559.7917-2-ard.biesheuvel@linaro.org
> Signed-off-by: Ingo Molnar <mingo at kernel.org>
> 
> (cherry picked from commit 4e78921ba4dd0aca1cc89168f45039add4183f8e)
> CVE-2019-12380
> Signed-off-by: Benjamin M Romer <benjamin.romer at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>
> ---

As noted by Kleber, to be applied to the source-only disco tree.

-Stefan

>  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 0c3be3ede87b..3304f61538a2 100644
> --- a/arch/x86/platform/efi/efi.c
> +++ b/arch/x86/platform/efi/efi.c
> @@ -85,6 +85,8 @@ 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 cf0347f61b21..08ce8177c3af 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)
> 


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