The patch titled Subject: fs/proc/kcore.c: use probe_kernel_read() instead of memcpy() has been removed from the -mm tree. Its filename was fs-proc-kcorec-use-probe_kernel_read-instead-of-memcpy.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Heiko Carstens <heiko.carstens@xxxxxxxxxx> Subject: fs/proc/kcore.c: use probe_kernel_read() instead of memcpy() df04abfd181a ("fs/proc/kcore.c: Add bounce buffer for ktext data") added a bounce buffer to avoid hardened usercopy checks. Copying to the bounce buffer was implemented with a simple memcpy() assuming that it is always valid to read from kernel memory iff the kern_addr_valid() check passed. A simple, but pointless, test case like "dd if=/proc/kcore of=/dev/null" now can easily crash the kernel, since the former execption handling on invalid kernel addresses now doesn't work anymore. Also adding a kern_addr_valid() implementation wouldn't help here. Most architectures simply return 1 here, while a couple implemented a page table walk to figure out if something is mapped at the address in question. With DEBUG_PAGEALLOC active mappings are established and removed all the time, so that relying on the result of kern_addr_valid() before executing the memcpy() also doesn't work. Therefore simply use probe_kernel_read() to copy to the bounce buffer. This also allows to simplify read_kcore(). At least on s390 this fixes the observed crashes and doesn't introduce warnings that were removed with df04abfd181a ("fs/proc/kcore.c: Add bounce buffer for ktext data"), even though the generic probe_kernel_read() implementation uses uaccess functions. While looking into this I'm also wondering if kern_addr_valid() could be completely removed...(?) Link: http://lkml.kernel.org/r/20171202132739.99971-1-heiko.carstens@xxxxxxxxxx Fixes: df04abfd181a ("fs/proc/kcore.c: Add bounce buffer for ktext data") Fixes: f5509cc18daa ("mm: Hardened usercopy") Signed-off-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx> Acked-by: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Jiri Olsa <jolsa@xxxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/proc/kcore.c | 18 +++++------------- 1 file changed, 5 insertions(+), 13 deletions(-) diff -puN fs/proc/kcore.c~fs-proc-kcorec-use-probe_kernel_read-instead-of-memcpy fs/proc/kcore.c --- a/fs/proc/kcore.c~fs-proc-kcorec-use-probe_kernel_read-instead-of-memcpy +++ a/fs/proc/kcore.c @@ -512,23 +512,15 @@ read_kcore(struct file *file, char __use return -EFAULT; } else { if (kern_addr_valid(start)) { - unsigned long n; - /* * Using bounce buffer to bypass the * hardened user copy kernel text checks. */ - memcpy(buf, (char *) start, tsz); - n = copy_to_user(buffer, buf, tsz); - /* - * We cannot distinguish between fault on source - * and fault on destination. When this happens - * we clear too and hope it will trigger the - * EFAULT again. - */ - if (n) { - if (clear_user(buffer + tsz - n, - n)) + if (probe_kernel_read(buf, (void *) start, tsz)) { + if (clear_user(buffer, tsz)) + return -EFAULT; + } else { + if (copy_to_user(buffer, buf, tsz)) return -EFAULT; } } else { _ Patches currently in -mm which might be from heiko.carstens@xxxxxxxxxx are