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commit cb22f247f371bd206a88cf0e0c05d80b8b62fb26 upstream.
The following testcase exposed a problem with our read access checks
in get_user() and raw_copy_from_user():
#include <stdint.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/mman.h>
#include <sys/types.h>
int main(int argc, char **argv)
{
unsigned long page_size = sysconf(_SC_PAGESIZE);
char *p = malloc(3 * page_size);
char *p_aligned;
/* initialize memory region. If not initialized, write syscall below will correctly return EFAULT. */
if (1)
memset(p, 'X', 3 * page_size);
p_aligned = (char *) ((((uintptr_t) p) + (2*page_size - 1)) & ~(page_size - 1));
/* Drop PROT_READ protection. Kernel and userspace should fault when accessing that memory region */
mprotect(p_aligned, page_size, PROT_NONE);
/* the following write() should return EFAULT, since PROT_READ was dropped by previous mprotect() */
int ret = write(2, p_aligned, 1);
if (!ret || errno != EFAULT)
printf("\n FAILURE: write() did not returned expected EFAULT value\n");
return 0;
}
Because of the way _PAGE_READ is handled, kernel code never generates
a read access fault when it access a page as the kernel privilege level
is always less than PL1 in the PTE.
This patch reworks the comments in the make_insert_tlb macro to try
to make this clearer.
Signed-off-by: John David Anglin <dave.anglin@bell.net>
Signed-off-by: Helge Deller <deller@gmx.de>
Cc: stable@vger.kernel.org # v5.12+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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.