On Mon, Sep 11, 2017 at 8:45 PM, Guenter Roeck <[email protected]> wrote: > Mainline crashes as follows when running nios2 images. > > On node 0 totalpages: 65536 > free_area_init_node: node 0, pgdat c8408fa0, node_mem_map c8726000 > Normal zone: 512 pages used for memmap > Normal zone: 0 pages reserved > Normal zone: 65536 pages, LIFO batch:15 > Unable to handle kernel NULL pointer dereference at virtual address 00000000 > ea = c8003cb0, ra = c81cbf40, cause = 15 > Kernel panic - not syncing: Oops > > Problem is seen because get_cycles() is called before the timer it depends > on is initialized. Returning 0 in that situation fixes the problem. > > Fixes: 33d72f3822d7 ("init/main.c: extract early boot entropy from the ..") > Cc: Laura Abbott <[email protected]> > Cc: Kees Cook <[email protected]> > Cc: Daniel Micay <[email protected]> > Signed-off-by: Guenter Roeck <[email protected]>
Reviewed-by: Kees Cook <[email protected]> -Kees > --- > Taking a stab at the problem. Fix works for my qemu test. > > arch/nios2/kernel/time.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/arch/nios2/kernel/time.c b/arch/nios2/kernel/time.c > index 645129aaa9a0..20e86209ef2e 100644 > --- a/arch/nios2/kernel/time.c > +++ b/arch/nios2/kernel/time.c > @@ -107,7 +107,10 @@ static struct nios2_clocksource nios2_cs = { > > cycles_t get_cycles(void) > { > - return nios2_timer_read(&nios2_cs.cs); > + /* Only read timer if it has been initialized */ > + if (nios2_cs.timer.base) > + return nios2_timer_read(&nios2_cs.cs); > + return 0; > } > EXPORT_SYMBOL(get_cycles); > > -- > 2.7.4 > -- Kees Cook Pixel Security
