Hi Ville,
On Tue, 13 Apr 2021 19:59:34 +0300 Ville Syrjälä wrote:
>
>
> On Tue, Apr 13, 2021 at 05:02:40PM +0800, Jisheng Zhang wrote:
> > I met below error during boot with i915 builtin if pass
> > "i915.mitigations=off":
> > [ 0.015589] Booting kernel: `off' invalid for parameter `i915.mitigations'
> >
> > The reason is slab subsystem isn't ready at that time, so kstrdup()
> > returns NULL. Fix this issue by using stack var instead of kstrdup().
> >
> > Fixes: 984cadea032b ("drm/i915: Allow the sysadmin to override security mitigations")
> > Signed-off-by: Jisheng Zhang <Jisheng.Zhang@xxxxxxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/i915_mitigations.c | 7 ++-----
> > 1 file changed, 2 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_mitigations.c b/drivers/gpu/drm/i915/i915_mitigations.c
> > index 84f12598d145..7dadf41064e0 100644
> > --- a/drivers/gpu/drm/i915/i915_mitigations.c
> > +++ b/drivers/gpu/drm/i915/i915_mitigations.c
> > @@ -29,15 +29,13 @@ bool i915_mitigate_clear_residuals(void)
> > static int mitigations_set(const char *val, const struct kernel_param *kp)
> > {
> > unsigned long new = ~0UL;
> > - char *str, *sep, *tok;
> > + char str[64], *sep, *tok;
> > bool first = true;
> > int err = 0;
> >
> > BUILD_BUG_ON(ARRAY_SIZE(names) >= BITS_PER_TYPE(mitigations));
> >
> > - str = kstrdup(val, GFP_KERNEL);
> > - if (!str)
> > - return -ENOMEM;
> > + strncpy(str, val, sizeof(str) - 1);
>
> I don't think strncpy() guarantees that the string is properly
> terminated.
>
> Also commit b1b6bed3b503 ("usb: core: fix quirks_param_set() writing to
> a const pointer") looks broken as well given your findings, and
> arch/um/drivers/virtio_uml.c seems to suffer from this as well.
> kernel/params.c itself seems to have some slab_is_available() magic
> around kmalloc().
Just tried the "usbcore.quirks" with usb builtin, I can't reproduce the
issue. Futher investigation shows that device_param_cb() macro is the
key, or the "6" in __level_param_cb(name, ops, arg, perm, 6) is the key.
While i915.mitigations uses module_param_cb_unsafe(), in which the level
will be "-1"
arch/um/drivers/virtio_uml.c also makes use of device_param_cb()
thanks
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