On 16/05/2019 15:16, Mark Rutland wrote: > On Thu, May 16, 2019 at 03:05:31PM +0100, Steven Price wrote: >> On 16/05/2019 14:41, Mark Rutland wrote: >>> On Thu, May 16, 2019 at 02:38:20PM +0100, Mark Rutland wrote: >>>> Hi, >>>> >>>> Since commit: >>>> >>>> 54c7a8916a887f35 ("initramfs: free initrd memory if opening >>>> /initrd.image fails") >>> >>> Ugh, I dropped a paragarph here. >>> >>> Since that commit, I'm seeing a boot-time splat on arm64 when using >>> CONFIG_DEBUG_VIRTUAL. I'm running an arm64 syzkaller instance, and this >>> kills the VM, preventing further testing, which is unfortunate. >>> >>> Mark. >>> >>>> IIUC prior to that commit, we'd only attempt to free an intird if we had >>>> one, whereas now we do so unconditionally. AFAICT, in this case >>>> initrd_start has not been initialized (I'm not using an initrd or >>>> initramfs on my system), so we end up trying virt_to_phys() on a bogus >>>> VA in free_initrd_mem(). >>>> >>>> Any ideas on the right way to fix this? >> >> Your analysis looks right to me. In my review I'd managed to spot the >> change in behaviour when CONFIG_INITRAMFS_FORCE is set (the initrd is >> freed), but I'd overlooked what happens if initrd_start == 0 (the >> non-existent initrd is attempted to be freed). >> >> I suspect the following is sufficient to fix the problem: >> >> ----8<----- >> diff --git a/init/initramfs.c b/init/initramfs.c >> index 435a428c2af1..178130fd61c2 100644 >> --- a/init/initramfs.c >> +++ b/init/initramfs.c >> @@ -669,7 +669,7 @@ static int __init populate_rootfs(void) >> * If the initrd region is overlapped with crashkernel reserved region, >> * free only memory that is not part of crashkernel region. >> */ >> - if (!do_retain_initrd && !kexec_free_initrd()) >> + if (!do_retain_initrd && initrd_start && !kexec_free_initrd()) >> free_initrd_mem(initrd_start, initrd_end); >> initrd_start = 0; >> initrd_end = 0; > > That works for me. If you spin this as a real patch: > > Tested-by: Mark Rutland <mark.rutl...@arm.com> > > As I mentioned, initrd_start has not been initialized at all, so I > suspect we should also update its declaration in init/do_mounts_initrd.c > such that it is guaranteed to be initialized to zero. We get away with > that today, but that won't necessarily hold with LTO and so on...
Well it's a global variable, so the C standard says it should be initialised to 0... I'll spin a real patch and add your Tested-by Steve