From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-x241.google.com (mail-io0-x241.google.com [IPv6:2607:f8b0:4001:c06::241]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3z95Hc5ZSKzDr51 for ; Mon, 1 Jan 2018 16:25:16 +1100 (AEDT) Received: by mail-io0-x241.google.com with SMTP id v30so14363403iov.7 for ; Sun, 31 Dec 2017 21:25:16 -0800 (PST) From: John Sperbeck To: Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , linuxppc-dev@lists.ozlabs.org Cc: John Sperbeck Subject: [PATCH] powerpc/mm: restore SEGV_ACCERR for segv on mapped region Date: Sun, 31 Dec 2017 21:24:58 -0800 Message-Id: <20180101052458.132027-1-jsperbeck@google.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , A recent refactoring of the powerpc page fault handler 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 change restores the previous behavior. The following program exhibits the issue: $ ./repro read || echo "FAILED" $ ./repro write || echo "FAILED" $ ./repro exec || echo "FAILED" #include #include #include #include #include #include #include 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 */ } Signed-off-by: John Sperbeck --- arch/powerpc/mm/fault.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) 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 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address, 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, -- 2.15.1.620.gb9897f4670-goog