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Message-ID: <2024120822-unnerving-childless-bf01@gregkh> Date: Sun, 8 Dec 2024 14:28:38 +0100 From: Greg KH <gregkh@...uxfoundation.org> To: Nilay Shroff <nilay@...ux.ibm.com> Cc: linux-kernel@...r.kernel.org, briannorris@...omium.org, kees@...nel.org, nathan@...nel.org, yury.norov@...il.com, steffen.klassert@...unet.com, daniel.m.jordan@...cle.com, linux-crypto@...r.kernel.org, linux@...ssschuh.net, gjoyce@....com Subject: Re: [PATCHv2] cpumask: work around false-postive stringop-overread errors On Sun, Dec 08, 2024 at 03:51:10PM +0530, Nilay Shroff wrote: > > > On 12/7/24 17:14, Greg KH wrote: > > On Sat, Dec 07, 2024 at 12:43:19PM +0100, Greg KH wrote: > >> On Thu, Dec 05, 2024 at 06:04:09PM +0530, Nilay Shroff wrote: > >>> While building the powerpc code using gcc 13, I came across following > >>> errors generated for kernel/padata.c file: > >>> > >>> CC kernel/padata.o > >>> In file included from ./include/linux/string.h:390, > >>> from ./arch/powerpc/include/asm/paca.h:16, > >>> from ./arch/powerpc/include/asm/current.h:13, > >>> from ./include/linux/thread_info.h:23, > >>> from ./include/asm-generic/preempt.h:5, > >>> from ./arch/powerpc/include/generated/asm/preempt.h:1, > >>> from ./include/linux/preempt.h:79, > >>> from ./include/linux/spinlock.h:56, > >>> from ./include/linux/swait.h:7, > >>> from ./include/linux/completion.h:12, > >>> from kernel/padata.c:14: > >>> In function ‘bitmap_copy’, > >>> inlined from ‘cpumask_copy’ at ./include/linux/cpumask.h:839:2, > >>> inlined from ‘__padata_set_cpumasks’ at kernel/padata.c:730:2: > >>> ./include/linux/fortify-string.h:114:33: error: ‘__builtin_memcpy’ reading between 257 and 536870904 bytes from a region of size 256 [-Werror=stringop-overread] > >>> 114 | #define __underlying_memcpy __builtin_memcpy > >>> | ^ > >>> ./include/linux/fortify-string.h:633:9: note: in expansion of macro ‘__underlying_memcpy’ > >>> 633 | __underlying_##op(p, q, __fortify_size); \ > >>> | ^~~~~~~~~~~~~ > >>> ./include/linux/fortify-string.h:678:26: note: in expansion of macro ‘__fortify_memcpy_chk’ > >>> 678 | #define memcpy(p, q, s) __fortify_memcpy_chk(p, q, s, \ > >>> | ^~~~~~~~~~~~~~~~~~~~ > >>> ./include/linux/bitmap.h:259:17: note: in expansion of macro ‘memcpy’ > >>> 259 | memcpy(dst, src, len); > >>> | ^~~~~~ > >>> kernel/padata.c: In function ‘__padata_set_cpumasks’: > >>> kernel/padata.c:713:48: note: source object ‘pcpumask’ of size [0, 256] > >>> 713 | cpumask_var_t pcpumask, > >>> | ~~~~~~~~~~~~~~^~~~~~~~ > >>> In function ‘bitmap_copy’, > >>> inlined from ‘cpumask_copy’ at ./include/linux/cpumask.h:839:2, > >>> inlined from ‘__padata_set_cpumasks’ at kernel/padata.c:730:2: > >>> ./include/linux/fortify-string.h:114:33: error: ‘__builtin_memcpy’ reading between 257 and 536870904 bytes from a region of size 256 [-Werror=stringop-overread] > >>> 114 | #define __underlying_memcpy __builtin_memcpy > >>> | ^ > >>> ./include/linux/fortify-string.h:633:9: note: in expansion of macro ‘__underlying_memcpy’ > >>> 633 | __underlying_##op(p, q, __fortify_size); \ > >>> | ^~~~~~~~~~~~~ > >>> ./include/linux/fortify-string.h:678:26: note: in expansion of macro ‘__fortify_memcpy_chk’ > >>> 678 | #define memcpy(p, q, s) __fortify_memcpy_chk(p, q, s, \ > >>> | ^~~~~~~~~~~~~~~~~~~~ > >>> ./include/linux/bitmap.h:259:17: note: in expansion of macro ‘memcpy’ > >>> 259 | memcpy(dst, src, len); > >>> | ^~~~~~ > >>> kernel/padata.c: In function ‘__padata_set_cpumasks’: > >>> kernel/padata.c:713:48: note: source object ‘pcpumask’ of size [0, 256] > >>> 713 | cpumask_var_t pcpumask, > >>> | ~~~~~~~~~~~~~~^~~~~~~~ > >>> > >>> Apparently, above errors only manifests with GCC 13.x and config option > >>> CONFIG_FORTIFY_SOURCE. Furthermore, if I use gcc 11.x or gcc 12.x then I > >>> don't encounter above errors. Prima facie, these errors appear to be false- > >>> positive. Brian informed me that currently some efforts are underway by > >>> GCC developers to emit more verbose information when GCC detects string > >>> overflow errors and that might help to further narrow down the root cause > >>> of this error. So for now, silence these errors using -Wno-stringop- > >>> overread gcc option while building kernel/padata.c file until we find the > >>> root cause. > >> > >> I'm hitting this now on Linus's tree using gcc14 on x86-64 so this isn't > >> just a problem with your arch. > Thanks Greg for confirming that this is not isolated to PowerPC!! > >> > >> Let me try this patch locally and see if it helps... > > > > Yes, fixes the build for me, so either this is a real fix, or something > > else needs to be done for it, so I'll give a: > > > > Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> > > > > for now. > Okay so now we've an evidence confirming that this is no longer PowerPC specific > issue. Hence as Yury suggested, in another mail[1], fixing this error by disabling > stringop-overread globally for GCC13+ and CONFIG_FORTIFY_SOURCE=n, I will spin a > new patch and submit it. > > [1] https://lore.kernel.org/all/Z1HTdtvNjm-nZSvJ@yury-ThinkPad/ That feels wrong, unless this is a compiler bug. And if it's a compiler bug, can we fix the compiler please or at least submit a bug to the gcc developers? I'm slowly moving all my boxes/builds over to using clang to build the kernel due to rust kernel work, so I guess I can do that here as well as I don't think this issue shows up for that compiler, right? thanks, greg k-h
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