Messages in this thread | | | Date | Fri, 11 Oct 2019 13:09:18 +0100 | From | Will Deacon <> | Subject | Re: [PATCH v3 06/10] lib/refcount: Move saturation warnings out of line |
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On Thu, Oct 10, 2019 at 01:48:20PM -0700, Kees Cook wrote: > On Mon, Oct 07, 2019 at 04:46:59PM +0100, Will Deacon wrote: > > Having the refcount saturation and warnings inline bloats the text, > > despite the fact that these paths should never be executed in normal > > operation. > > > > Move the refcount saturation and warnings out of line to reduce the > > image size when refcount_t checking is enabled. Relative to an x86_64 > > defconfig, the sizes reported by bloat-o-meter are: > > > > # defconfig+REFCOUNT_FULL, inline saturation (i.e. before this patch) > > Total: Before=14762076, After=14915442, chg +1.04% > > > > # defconfig+REFCOUNT_FULL, out-of-line saturation (i.e. after this patch) > > Total: Before=14762076, After=14835497, chg +0.50% > > The downside of this change is that this means we get one warning per > refcount_saturation_type, where as before it was once per refcount > usage. I think, ultimately, this is okay, but it is a behavioral change > that might be worth pointing out.
Good point; I'll add something to the commit message.
> > diff --git a/lib/refcount.c b/lib/refcount.c > > index 3a534fbebdcc..6a61d39f9390 100644 > > --- a/lib/refcount.c > > +++ b/lib/refcount.c > > @@ -8,6 +8,34 @@ > > #include <linux/spinlock.h> > > #include <linux/bug.h> > > > > +#define REFCOUNT_WARN(str) WARN_ONCE(1, "refcount_t: " str ".\n") > > This define seems like overkill for just adding a prefix to 5 uses...
I dunno. It doesn't hurt and I did get bored of typing that prefix.
> > +void refcount_warn_saturate(refcount_t *r, enum refcount_saturation_type t) > > +{ > > + refcount_set(r, REFCOUNT_SATURATED); > > + > > + switch (t) { > > + case REFCOUNT_ADD_NOT_ZERO_OVF: > > + REFCOUNT_WARN("saturated; leaking memory"); > > + break; > > + case REFCOUNT_ADD_OVF: > > + REFCOUNT_WARN("saturated; leaking memory"); > > + break; > > + case REFCOUNT_ADD_UAF: > > + REFCOUNT_WARN("addition on 0; use-after-free"); > > + break; > > + case REFCOUNT_SUB_UAF: > > + REFCOUNT_WARN("underflow; use-after-free"); > > + break; > > + case REFCOUNT_DEC_LEAK: > > + REFCOUNT_WARN("decrement hit 0; leaking memory"); > > Even the longest doesn't line wrap: > > WARN_ONCE(1, "refcount_t: decrement hit 0; leaking memory\n"); > > > + break; > > + default: > > + WARN_ON(1); > > This deserves a string too, yes? > > WARN_ONCE(1, "refcount_t: unknown saturation event!?\n");
Ok.
> > > + } > > +} > > +EXPORT_SYMBOL(refcount_warn_saturate); > > + > > /** > > * refcount_dec_if_one - decrement a refcount if it is 1 > > * @r: the refcount > > -- > > 2.23.0.581.g78d2f28ef7-goog > > > > Otherwise, okay, I grudgingly accept the loss of warnings when running > the lkdtm tests in order to gain back some text size... :)
Thanks :)
Will
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