Re: [kvm-unit-tests PATCH] x86: Fix breakage of fw_cfg for 32-bit unit tests

[Sean Christopherson <sean.j.christopherson@intel.com>]

On Thu, Aug 22, 2019 at 04:55:14PM -0700, Nadav Amit wrote:
> > On Aug 22, 2019, at 4:50 PM, Sean Christopherson <sean.j.christopherson@intel.com> wrote:
> > 
> > Ensure the fw_cfg overrides are parsed prior consuming any of said
> > overrides.  fwcfg_get_u() treats zero as a valid overide value, which
> > is slightly problematic since the overrides are in the .bss and thus
> > initialized to zero.
> > 
> > Add a limit check when indexing fw_override so that future code doesn't
> > spontaneously explode.
> > 
> > Cc: Nadav Amit <nadav.amit@gmail.com>
> > Fixes: 03b1e4570f967 ("x86: Support environments without test-devices")
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > ---
> > lib/x86/fwcfg.c | 10 ++++++++--
> > lib/x86/fwcfg.h |  2 --
> > x86/cstart64.S  |  2 --
> > 3 files changed, 8 insertions(+), 6 deletions(-)
> > 
> > diff --git a/lib/x86/fwcfg.c b/lib/x86/fwcfg.c
> > index d8d797f..06ef62c 100644
> > --- a/lib/x86/fwcfg.c
> > +++ b/lib/x86/fwcfg.c
> > @@ -5,10 +5,11 @@
> > static struct spinlock lock;
> > 
> > static long fw_override[FW_CFG_MAX_ENTRY];
> > +static bool fw_override_done;
> > 
> > bool no_test_device;
> > 
> > -void read_cfg_override(void)
> > +static void read_cfg_override(void)
> > {
> > 	const char *str;
> > 	int i;
> > @@ -26,6 +27,8 @@ void read_cfg_override(void)
> > 
> > 	if ((str = getenv("TEST_DEVICE")))
> > 		no_test_device = !atol(str);
> > +
> > +    fw_override_done = true;
> > }
> > 
> > static uint64_t fwcfg_get_u(uint16_t index, int bytes)
> > @@ -34,7 +37,10 @@ static uint64_t fwcfg_get_u(uint16_t index, int bytes)
> >     uint8_t b;
> >     int i;
> > 
> > -    if (fw_override[index] >= 0)
> > +    if (!fw_override_done)
> > +        read_cfg_override();
> > +
> > +    if (index < FW_CFG_MAX_ENTRY && fw_override[index] >= 0)
> > 	    return fw_override[index];
> 
> How did that happen? I remember I tested this code with KVM..

It only breaks 32-bit KVM.