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Baoquan He reported lots of KFENCE reports when /proc/kcore is read, e.g. with crash or even simpler with dd: BUG: KFENCE: invalid read in copy_from_kernel_nofault+0x5e/0x120 Invalid read at 0x00000000f4f5149f: copy_from_kernel_nofault+0x5e/0x120 read_kcore+0x6b2/0x870 proc_reg_read+0x9a/0xf0 vfs_read+0x94/0x270 ksys_read+0x70/0x100 __do_syscall+0x1d0/0x200 system_call+0x82/0xb0 The reason for this is that read_kcore() simply reads memory that might have been unmapped by KFENCE with copy_from_kernel_nofault(). Any fault due to pages being unmapped by KFENCE would be handled gracefully by the fault handler (exception table fixup). However the s390 fault handler first reports the fault, and only afterwards would perform the exception table fixup. Most architectures have this in reversed order, which also avoids the false positive KFENCE reports when an unmapped page is accessed. Therefore change the s390 fault handler so it handles exception table fixups before KFENCE page faults are reported. Reported-by: Baoquan He <bhe@redhat.com> Tested-by: Baoquan He <bhe@redhat.com> Acked-by: Alexander Potapenko <glider@google.com> Link: https://lore.kernel.org/r/20230213183858.1473681-1-hca@linux.ibm.com Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.