Messages in this thread Patch in this message | | | Date | Tue, 21 May 2019 10:57:59 +0800 | From | Gen Zhang <> | Subject | Re: [PATCH v2] efi_64: Fix a missing-check bug in arch/x86/platform/efi/efi_64.c |
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On Fri, May 17, 2019 at 11:24:27AM +0200, Ard Biesheuvel wrote: > On Fri, 17 May 2019 at 11:06, Gen Zhang <blackgod016574@gmail.com> wrote: > > > > On Fri, May 17, 2019 at 10:41:28AM +0200, Ard Biesheuvel wrote: > > > Returning an error here is not going to make much difference, given > > > that the caller of efi_call_phys_prolog() does not bother to check it, > > > and passes the result straight into efi_call_phys_epilog(), which > > > happily attempts to dereference it. > > > > > > So if you want to fix this properly, please fix it at the call site as > > > well. I'd prefer to avoid ERR_PTR() and just return NULL for a failed > > > allocation though. > > Hi Ard, > > Thanks for your timely reply! > > I think returning NULL in efi_call_phys_prolog() and checking in > > efi_call_phys_epilog() is much better. But I am confused what to return > > in efi_call_phys_epilog() if save_pgd is NULL. Definitely not return > > -ENOMEM, because efi_call_phys_epilog() returns unsigned long. Could > > please light on me to fix this problem? > > > If efi_call_phys_prolog() returns NULL, the calling function should > abort and never call efi_call_phys_epilog(). In efi_call_phys_prolog(), 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. Further, if efi_call_phys_prolog() returns NULL, we should abort the process in phys_efi_set_virtual_address_map(), and return EFI_ABORTED.
Signed-off-by: Gen Zhang <blackgod016574@gmail.com>
--- 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 ---
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