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John Sperbeck ecb101aed8 powerpc/mm: Fix SEGV on mapped region to return SEGV_ACCERR 
The recent refactoring of the powerpc page fault handler in commit
c3350602e8 ("powerpc/mm: Make bad_area* helper functions") caused
access to protected memory regions to indicate SEGV_MAPERR instead of
the traditional SEGV_ACCERR in the si_code field of a user-space
signal handler. This can confuse debug libraries that temporarily
change the protection of memory regions, and expect to use SEGV_ACCERR
as an indication to restore access to a region.

This commit restores the previous behavior. The following program
exhibits the issue:

    $ ./repro read  || echo "FAILED"
    $ ./repro write || echo "FAILED"
    $ ./repro exec  || echo "FAILED"

    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #include <unistd.h>
    #include <signal.h>
    #include <sys/mman.h>
    #include <assert.h>

    static void segv_handler(int n, siginfo_t *info, void *arg) {
            _exit(info->si_code == SEGV_ACCERR ? 0 : 1);
    }

    int main(int argc, char **argv)
    {
            void *p = NULL;
            struct sigaction act = {
                    .sa_sigaction = segv_handler,
                    .sa_flags = SA_SIGINFO,
            };

            assert(argc == 2);
            p = mmap(NULL, getpagesize(),
                    (strcmp(argv[1], "write") == 0) ? PROT_READ : 0,
                    MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
            assert(p != MAP_FAILED);

            assert(sigaction(SIGSEGV, &act, NULL) == 0);
            if (strcmp(argv[1], "read") == 0)
                    printf("%c", *(unsigned char *)p);
            else if (strcmp(argv[1], "write") == 0)
                    *(unsigned char *)p = 0;
            else if (strcmp(argv[1], "exec") == 0)
                    ((void (*)(void))p)();
            return 1;  /* failed to generate SEGV */
    }

Fixes: c3350602e8 ("powerpc/mm: Make bad_area* helper functions")
Cc: stable@vger.kernel.org # v4.14+
Signed-off-by: John Sperbeck <jsperbeck@google.com>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
[mpe: Add commit references in change log]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
 		2018-01-02 21:12:33 +11:00
..
alpha treewide: setup_timer() -> timer_setup() 2017-11-21 15:57:07 -08:00
arc ARC updates for 4.15-rc1 2017-11-25 08:21:54 -10:00
arm Merge branch 'fixes' of git://git.armlinux.org.uk/~rmk/linux-arm 2017-12-03 10:51:08 -05:00
arm64 arm64 fixes: 2017-12-01 19:37:03 -05:00
blackfin treewide: setup_timer() -> timer_setup() 2017-11-21 15:57:07 -08:00
c6x Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
cris pci-v4.15-changes 2017-11-15 15:01:28 -08:00
frv Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
h8300 mm, arch: remove empty_bad_page* 2017-11-15 18:21:03 -08:00
hexagon Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
ia64 arch/ia64/include/asm/topology.h: remove unused parent_node() macro 2017-11-17 16:10:04 -08:00
m32r m32r: fix endianness constraints 2017-11-15 18:21:00 -08:00
m68k m68k/macboing: Fix missed timer callback assignment 2017-11-24 16:19:40 +01:00
metag DeviceTree for 4.15: 2017-11-14 18:25:40 -08:00
microblaze Microblaze patch for 4.15-rc2 2017-11-29 14:19:22 -08:00
mips * x86 bugfixes: APIC, nested virtualization, IOAPIC 2017-11-30 08:15:19 -08:00
mn10300 bug: define the "cut here" string in a single place 2017-11-17 16:10:01 -08:00
nios2 DeviceTree for 4.15: 2017-11-14 18:25:40 -08:00
openrisc kmemcheck: remove annotations 2017-11-15 18:21:04 -08:00
parisc treewide: Switch DEFINE_TIMER callbacks to struct timer_list * 2017-11-21 15:57:05 -08:00
powerpc powerpc/mm: Fix SEGV on mapped region to return SEGV_ACCERR 2018-01-02 21:12:33 +11:00
riscv RISC-V: Fixes for clean allmodconfig build 2017-12-01 13:31:31 -08:00
s390 * x86 bugfixes: APIC, nested virtualization, IOAPIC 2017-11-30 08:15:19 -08:00
score License cleanup: add SPDX license identifier to uapi header files with no license 2017-11-02 11:19:54 +01:00
sh treewide: setup_timer() -> timer_setup() 2017-11-21 15:57:07 -08:00
sparc Merge branch 'akpm' (patches from Andrew) 2017-11-29 19:12:44 -08:00
tile mm: switch to 'define pmd_write' instead of __HAVE_ARCH_PMD_WRITE 2017-11-29 18:40:42 -08:00
um This pull request contains the following core changes: 2017-11-22 20:46:06 -10:00
unicore32 kmemcheck: stop using GFP_NOTRACK and SLAB_NOTRACK 2017-11-15 18:21:04 -08:00
x86 * x86 bugfixes: APIC, nested virtualization, IOAPIC 2017-11-30 08:15:19 -08:00
xtensa libnvdimm for 4.15 2017-11-17 09:51:57 -08:00
.gitignore
…
Kconfig bpf: Revert bpf_overrid_function() helper changes. 2017-11-11 18:24:55 +09:00