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authorJohn Sperbeck <jsperbeck@google.com>2017-12-31 21:24:58 -0800
committerMichael Ellerman <mpe@ellerman.id.au>2018-01-02 21:12:33 +1100
commitecb101aed86156ec7cd71e5dca668e09146e6994 (patch)
parent7333b5aca412d6ad02667b5a513485838a91b136 (diff)
powerpc/mm: Fix SEGV on mapped region to return SEGV_ACCERR
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") 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>
1 files changed, 6 insertions, 1 deletions
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 4797d08581ce..6e1e39035380 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -145,6 +145,11 @@ static noinline int bad_area(struct pt_regs *regs, unsigned long address)
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:
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,