From 6c57d320484988e87e446e2e60ce42816bf51d53 Mon Sep 17 00:00:00 2001 From: "H.J. Lu" Date: Mon, 1 Feb 2021 11:00:38 -0800 Subject: sysconf: Add _SC_MINSIGSTKSZ/_SC_SIGSTKSZ [BZ #20305] Add _SC_MINSIGSTKSZ for the minimum signal stack size derived from AT_MINSIGSTKSZ, which is the minimum number of bytes of free stack space required in order to gurantee successful, non-nested handling of a single signal whose handler is an empty function, and _SC_SIGSTKSZ which is the suggested minimum number of bytes of stack space required for a signal stack. If AT_MINSIGSTKSZ isn't available, sysconf (_SC_MINSIGSTKSZ) returns MINSIGSTKSZ. On Linux/x86 with XSAVE, the signal frame used by kernel is composed of the following areas and laid out as: ------------------------------ | alignment padding | ------------------------------ | xsave buffer | ------------------------------ | fsave header (32-bit only) | ------------------------------ | siginfo + ucontext | ------------------------------ Compute AT_MINSIGSTKSZ value as size of xsave buffer + size of fsave header (32-bit only) + size of siginfo and ucontext + alignment padding. If _SC_SIGSTKSZ_SOURCE or _GNU_SOURCE are defined, MINSIGSTKSZ and SIGSTKSZ are redefined as /* Default stack size for a signal handler: sysconf (SC_SIGSTKSZ). */ # undef SIGSTKSZ # define SIGSTKSZ sysconf (_SC_SIGSTKSZ) /* Minimum stack size for a signal handler: SIGSTKSZ. */ # undef MINSIGSTKSZ # define MINSIGSTKSZ SIGSTKSZ Compilation will fail if the source assumes constant MINSIGSTKSZ or SIGSTKSZ. The reason for not simply increasing the kernel's MINSIGSTKSZ #define (apart from the fact that it is rarely used, due to glibc's shadowing definitions) was that userspace binaries will have baked in the old value of the constant and may be making assumptions about it. For example, the type (char [MINSIGSTKSZ]) changes if this #define changes. This could be a problem if an newly built library tries to memcpy() or dump such an object defined by and old binary. Bounds-checking and the stack sizes passed to things like sigaltstack() and makecontext() could similarly go wrong. --- signal/Makefile | 5 +-- signal/signal.h | 1 + signal/tst-minsigstksz-5.c | 84 ++++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 88 insertions(+), 2 deletions(-) create mode 100644 signal/tst-minsigstksz-5.c (limited to 'signal') diff --git a/signal/Makefile b/signal/Makefile index e89c308889..3d8cab1f50 100644 --- a/signal/Makefile +++ b/signal/Makefile @@ -31,7 +31,8 @@ headers := signal.h sys/signal.h \ bits/types/sigevent_t.h bits/types/siginfo_t.h \ bits/types/sigset_t.h bits/types/sigval_t.h \ bits/types/stack_t.h bits/types/struct_sigstack.h \ - bits/types/__sigval_t.h bits/signal_ext.h + bits/types/__sigval_t.h bits/signal_ext.h \ + bits/sigstksz.h routines := signal raise killpg \ sigaction sigprocmask kill \ @@ -48,7 +49,7 @@ routines := signal raise killpg \ tests := tst-signal tst-sigset tst-sigsimple tst-raise tst-sigset2 \ tst-sigwait-eintr tst-sigaction \ tst-minsigstksz-1 tst-minsigstksz-2 tst-minsigstksz-3 \ - tst-minsigstksz-3a tst-minsigstksz-4 \ + tst-minsigstksz-3a tst-minsigstksz-4 tst-minsigstksz-5 \ tst-sigisemptyset include ../Rules diff --git a/signal/signal.h b/signal/signal.h index 6463c98e11..b17203c99c 100644 --- a/signal/signal.h +++ b/signal/signal.h @@ -312,6 +312,7 @@ extern int siginterrupt (int __sig, int __interrupt) __THROW __attribute_deprecated_msg__ ("Use sigaction with SA_RESTART instead"); # include +# include # include /* Alternate signal handler stack interface. diff --git a/signal/tst-minsigstksz-5.c b/signal/tst-minsigstksz-5.c new file mode 100644 index 0000000000..d657d2f4e6 --- /dev/null +++ b/signal/tst-minsigstksz-5.c @@ -0,0 +1,84 @@ +/* Test of signal delivery on an alternate stack with MINSIGSTKSZ size. + Copyright (C) 2020 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +#include +#include +#include +#include +#include +#include + +static volatile sig_atomic_t handler_run; + +static void +handler (int signo) +{ + /* Clear a bit of on-stack memory. */ + volatile char buffer[256]; + for (size_t i = 0; i < sizeof (buffer); ++i) + buffer[i] = 0; + handler_run = 1; +} + +int +do_test (void) +{ + size_t stack_buffer_size = 64 * 1024 * 1024; + void *stack_buffer = xmalloc (stack_buffer_size); + void *stack_end = stack_buffer + stack_buffer_size; + memset (stack_buffer, 0xCC, stack_buffer_size); + + void *stack_bottom = stack_buffer + (stack_buffer_size + MINSIGSTKSZ) / 2; + void *stack_top = stack_bottom + MINSIGSTKSZ; + stack_t stack = + { + .ss_sp = stack_bottom, + .ss_size = MINSIGSTKSZ, + }; + if (sigaltstack (&stack, NULL) < 0) + FAIL_RET ("sigaltstack: %m\n"); + + struct sigaction act = + { + .sa_handler = handler, + .sa_flags = SA_ONSTACK, + }; + if (sigaction (SIGUSR1, &act, NULL) < 0) + FAIL_RET ("sigaction: %m\n"); + + if (kill (getpid (), SIGUSR1) < 0) + FAIL_RET ("kill: %m\n"); + + if (handler_run != 1) + FAIL_RET ("handler did not run\n"); + + for (void *p = stack_buffer; p < stack_bottom; ++p) + if (*(unsigned char *) p != 0xCC) + FAIL_RET ("changed byte %ld bytes below configured stack\n", + (long) (stack_bottom - p)); + for (void *p = stack_top; p < stack_end; ++p) + if (*(unsigned char *) p != 0xCC) + FAIL_RET ("changed byte %ld bytes above configured stack\n", + (long) (p - stack_top)); + + free (stack_buffer); + + return 0; +} + +#include -- cgit 1.4.1