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Date: Tue, 17 May 2022 14:15:41 0700 From: Kees Cook <keescook@...omium.org> To: Rasmus Villemoes <linux@...musvillemoes.dk> Cc: Yury Norov <yury.norov@...il.com>, Christophe de Dinechin <dinechin@...hat.com>, Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Andrew Morton <akpm@...uxfoundation.org>, Zhen Lei <thunder.leizhen@...wei.com>, linuxkernel@...r.kernel.org, linuxhardening@...r.kernel.org Subject: Re: [PATCH] bitmap: Fix return values to be unsigned On Tue, May 17, 2022 at 08:49:38AM +0200, Rasmus Villemoes wrote: > On 17/05/2022 05.54, Kees Cook wrote: > > Both nodemask and bitmap routines had mixed return values that provided > > potentially signed results that could never happen. This was leading to > > the compiler getting confusing about the range of possible return values > > (it was thinking things could be negative where they could not be). Fix > > all the nodemask and bitmap routines that should be returning unsigned > > (or bool) values. Silences GCC 12 warnings: > > So, for the bitmap functions themselves, makes sense, and then also for > the nodemask functions which are merely wrappers around the bitmap > functions (or wrappers around wrappers ...). But see below. Cool. I think I should split this into two patches. > > > > > #define first_node(src) __first_node(&(src)) > > static inline int __first_node(const nodemask_t *srcp) > > +static inline unsigned int __first_node(const nodemask_t *srcp) > > { > >  return min_t(int, MAX_NUMNODES, find_first_bit(srcp>bits, MAX_NUMNODES)); > > + return min_t(unsigned int, MAX_NUMNODES, find_first_bit(srcp>bits, MAX_NUMNODES)); > > } > > Unrelated to the type change, but what's that min() doing there in the > first place? Doesn't find_first_bit() already return the nbits argument > if no "first bit" exists (i.e., the bitmap is empty)? > > > #define next_node(n, src) __next_node((n), &(src)) > > static inline int __next_node(int n, const nodemask_t *srcp) > > +static inline unsigned int __next_node(int n, const nodemask_t *srcp) > > { > >  return min_t(int,MAX_NUMNODES,find_next_bit(srcp>bits, MAX_NUMNODES, n+1)); > > + return min_t(unsigned int, MAX_NUMNODES, find_next_bit(srcp>bits, MAX_NUMNODES, n+1)); > > } > > Same here and a few more places. > > It seems to go all the way back to pregit. Hm. Could be cleaned up > separately I guess. Yeah, all I find as a hint is: /* FIXME: better would be to fix all architectures to never return > MAX_NUMNODES, then the silly min_ts could be dropped. */ which also predates git history. > > > > > #if defined(CONFIG_NUMA) && (MAX_NUMNODES > 1) > > extern int node_random(const nodemask_t *maskp); > > +extern unsigned int node_random(const nodemask_t *maskp); > > So this one I'm not convinced about. It has a documented return value of > NUMA_NO_NODE aka 1 if the mask is empty. And since it's not a wrapper > around a corresponding bitmap_random() (which would presumably, did it > exist, use the "return nbits if empty" convention), there's no > compelling reason to make its return type unsigned. Agreed; I'll drop this change. Thanks!  Kees Cook
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