This is a note to let you know that I've just added the patch titled

powerpc/mm: Fix SEGV on mapped region to return SEGV_ACCERR

to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: powerpc-mm-fix-segv-on-mapped-region-to-return-segv_accerr.patch and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From ecb101aed86156ec7cd71e5dca668e09146e6994 Mon Sep 17 00:00:00 2001

From: John Sperbeck jsperbeck@google.com Date: Sun, 31 Dec 2017 21:24:58 -0800 Subject: powerpc/mm: Fix SEGV on mapped region to return SEGV_ACCERR

From: John Sperbeck jsperbeck@google.com

commit ecb101aed86156ec7cd71e5dca668e09146e6994 upstream.

The recent refactoring of the powerpc page fault handler in commit c3350602e876 ("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: c3350602e876 ("powerpc/mm: Make bad_area* helper functions") 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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- arch/powerpc/mm/fault.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/arch/powerpc/mm/fault.c +++ b/arch/powerpc/mm/fault.c @@ -145,6 +145,11 @@ static noinline int bad_area(struct pt_r return __bad_area(regs, address, SEGV_MAPERR); }

+static noinline int bad_access(struct pt_regs *regs, unsigned long address) +{ + return __bad_area(regs, address, SEGV_ACCERR); +} + static int do_sigbus(struct pt_regs *regs, unsigned long address, unsigned int fault) { @@ -490,7 +495,7 @@ retry:

good_area: if (unlikely(access_error(is_write, is_exec, vma))) - return bad_area(regs, address); + return bad_access(regs, address);

/* * If for any reason at all we couldn't handle the fault,

Patches currently in stable-queue which might be from jsperbeck@google.com are

queue-4.14/powerpc-mm-fix-segv-on-mapped-region-to-return-segv_accerr.patch