Re: [PATCH] x86, kdump: Fix efi=noruntime NULL pointer dereference

[Dave Young]

On 08/09/18 at 09:33am, Mike Galbraith wrote:
> On Thu, 2018-08-09 at 12:21 +0800, Dave Young wrote:
> > Hi Mike,
> > 
> > Thanks for the patch!
> > On 08/08/18 at 04:03pm, Mike Galbraith wrote:
> > > When booting with efi=noruntime, we call efi_runtime_map_copy() while
> > > loading the kdump kernel, and trip over a NULL efi.memmap.map.  Avoid
> > > that and a useless allocation when the only mapping we can use (1:1)
> > > is not available.
> > 
> > At first glance, efi_get_runtime_map_size should return 0 in case
> > noruntime.
> 
> What efi does internally at unmap time is to leave everything except
> efi.mmap.map untouched, setting it to NULL and turning off EFI_MEMMAP,
> rendering efi.mmap.map accessors useless/unsafe without first checking
> EFI_MEMMAP.

Probably the x86 efi_init should reset nr_map to zero in case runtime is
disabled.  But let's see how Ard thinks about this and cc linux-efi.

As for efi_get_runtime_map_size, it was introduced for x86 kexec use.
for copying runtime maps,  so I think it is reasonable this function
return zero in case no runtime.

Thanks
Dave