On 12/8/24 18:58, Greg KH wrote: > 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@xxxxxxxxxxxxxxxxxxx> >>> >>> 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? > Yes this seems to be a compiler bug. Please see here : [1] https://lore.kernel.org/all/202411021337.85E9BB06@keescook/ [2] https://gcc.gnu.org/pipermail/gcc-patches/2024-October/666872.html > 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? > Yes this error doesn't show up for LLVM/clang. We've two options here: 1) To disable this error globally for GCC-13+ until we find the root cause. Maybe when GCC folks add more diagnostics and contexts around -Wstringop-* compiler warning as discussed in [2] above. or 2) Silence this error only for file kernel/padata.c compiling which this error manifests as of today. Yury suggested option #1 above so that we may avoid random victims hitting this error. What do you suggest? Thanks, --Nilay
