Re: [PATCH] efi_64: Fix a missing-check bug in arch/x86/platform/efi/efi_64.c of Linux 5.1

[Gen Zhang]

On Fri, May 17, 2019 at 11:24:27AM +0200, Ard Biesheuvel wrote:
> If efi_call_phys_prolog() returns NULL, the calling function should
> abort and never call efi_call_phys_epilog().
Hi Ard,
I edit the patch and it is as following. Returning EFI_ABORTED would
be proper, because the return value (status) is checked in 
__efi_enter_virtual_mode(). And returning EFI_ABORTED can abort the 
process.
Thanks
Gen



save_pgd is allocated by kmalloc_array. And it is dereferenced in the
following codes. However, memory allocation functions such as
kmalloc_array may fail. Dereferencing this save_pgd null pointer may 
cause the kernel go wrong. Thus we should check this allocation.

Signed-off-by: Gen Zhang <blackgod016574@xxxxxxxxx>

---
diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
index e1cb01a..a7189a3 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 cf0347f..828460a 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -91,6 +91,8 @@ pgd_t * __init efi_call_phys_prolog(void)
 
 	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
---