diff options
| -rw-r--r-- | support/Makefile | 1 | ||||
| -rw-r--r-- | support/support.h | 19 | ||||
| -rw-r--r-- | support/support_stack_alloc.c | 82 | ||||
| -rw-r--r-- | support/xsigstack.c | 43 |
4 files changed, 107 insertions, 38 deletions
diff --git a/support/Makefile b/support/Makefile index 5c69f0d..a462781 100644 --- a/support/Makefile +++ b/support/Makefile @@ -39,6 +39,7 @@ libsupport-routines = \ resolv_response_context_free \ resolv_test \ set_fortify_handler \ + support_stack_alloc \ support-xfstat \ support-xfstat-time64 \ support-xstat \ diff --git a/support/support.h b/support/support.h index 9ec8ecb..dbd270c 100644 --- a/support/support.h +++ b/support/support.h @@ -164,6 +164,25 @@ timer_t support_create_timer (uint64_t sec, long int nsec, bool repeat, /* Disable the timer TIMER. */ void support_delete_timer (timer_t timer); +struct support_stack +{ + void *stack; + size_t size; + size_t guardsize; +}; + +/* Allocate stack suitable to used with xclone or sigaltstack call. The stack + will have a minimum size of SIZE + MINSIGSTKSZ bytes, rounded up to a whole + number of pages. There will be a large (at least 1 MiB) inaccessible guard + bands on either side of it. + The returned value on ALLOC_BASE and ALLOC_SIZE will be the usable stack + region, excluding the GUARD_SIZE allocated area. + It also terminates the process on error. */ +struct support_stack support_stack_alloc (size_t size); + +/* Deallocate the STACK. */ +void support_stack_free (struct support_stack *stack); + __END_DECLS #endif /* SUPPORT_H */ diff --git a/support/support_stack_alloc.c b/support/support_stack_alloc.c new file mode 100644 index 0000000..03494dd --- /dev/null +++ b/support/support_stack_alloc.c @@ -0,0 +1,82 @@ +/* Allocate a stack suitable to be used with xclone or xsigaltstack. + Copyright (C) 2021 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 + <https://www.gnu.org/licenses/>. */ + +#include <support/check.h> +#include <support/support.h> +#include <support/xunistd.h> +#include <stdint.h> +#include <string.h> +#include <stackinfo.h> +#include <sys/mman.h> +#include <sys/param.h> /* roundup, MAX */ + +#ifndef MAP_NORESERVE +# define MAP_NORESERVE 0 +#endif +#ifndef MAP_STACK +# define MAP_STACK 0 +#endif + +struct support_stack +support_stack_alloc (size_t size) +{ + size_t pagesize = sysconf (_SC_PAGESIZE); + if (pagesize == -1) + FAIL_EXIT1 ("sysconf (_SC_PAGESIZE): %m\n"); + + /* Always supply at least MINSIGSTKSZ space; passing 0 as size means + only that much space. No matter what the number is, round it up + to a whole number of pages. */ + size_t stacksize = roundup (size + MINSIGSTKSZ, pagesize); + + /* The guard bands need to be large enough to intercept offset + accesses from a stack address that might otherwise hit another + mapping. Make them at least twice as big as the stack itself, to + defend against an offset by the entire size of a large + stack-allocated array. The minimum is 1MiB, which is arbitrarily + chosen to be larger than any "typical" wild pointer offset. + Again, no matter what the number is, round it up to a whole + number of pages. */ + size_t guardsize = roundup (MAX (2 * stacksize, 1024 * 1024), pagesize); + size_t alloc_size = guardsize + stacksize + guardsize; + /* Use MAP_NORESERVE so that RAM will not be wasted on the guard + bands; touch all the pages of the actual stack before returning, + so we know they are allocated. */ + void *alloc_base = xmmap (0, + alloc_size, + PROT_NONE, + MAP_PRIVATE|MAP_ANONYMOUS|MAP_NORESERVE|MAP_STACK, + -1); + /* Some architecture still requires executable stack for the signal return + trampoline, although PF_X could be overridden if PT_GNU_STACK is present. + However since glibc does not export such information with a proper ABI, + it uses the historical permissions. */ + int prot = PROT_READ | PROT_WRITE + | (DEFAULT_STACK_PERMS & PF_X ? PROT_EXEC : 0); + xmprotect (alloc_base + guardsize, stacksize, prot); + memset (alloc_base + guardsize, 0xA5, stacksize); + return (struct support_stack) { alloc_base + guardsize, stacksize, guardsize }; +} + +void +support_stack_free (struct support_stack *stack) +{ + void *alloc_base = (void *)((uintptr_t) stack->stack - stack->guardsize); + size_t alloc_size = stack->size + 2 * stack->guardsize; + xmunmap (alloc_base, alloc_size); +} diff --git a/support/xsigstack.c b/support/xsigstack.c index a2f0e32..a471c85 100644 --- a/support/xsigstack.c +++ b/support/xsigstack.c @@ -37,8 +37,7 @@ structures. */ struct sigstack_desc { - void *alloc_base; /* Base address of the complete allocation. */ - size_t alloc_size; /* Size of the complete allocation. */ + struct support_stack stack; stack_t alt_stack; /* The address and size of the stack itself. */ stack_t old_stack; /* The previous signal stack. */ }; @@ -46,43 +45,11 @@ struct sigstack_desc void * xalloc_sigstack (size_t size) { - size_t pagesize = sysconf (_SC_PAGESIZE); - if (pagesize == -1) - FAIL_EXIT1 ("sysconf (_SC_PAGESIZE): %m\n"); - - /* Always supply at least MINSIGSTKSZ space; passing 0 as size means - only that much space. No matter what the number is, round it up - to a whole number of pages. */ - size_t stacksize = roundup (size + MINSIGSTKSZ, pagesize); - - /* The guard bands need to be large enough to intercept offset - accesses from a stack address that might otherwise hit another - mapping. Make them at least twice as big as the stack itself, to - defend against an offset by the entire size of a large - stack-allocated array. The minimum is 1MiB, which is arbitrarily - chosen to be larger than any "typical" wild pointer offset. - Again, no matter what the number is, round it up to a whole - number of pages. */ - size_t guardsize = roundup (MAX (2 * stacksize, 1024 * 1024), pagesize); - struct sigstack_desc *desc = xmalloc (sizeof (struct sigstack_desc)); - desc->alloc_size = guardsize + stacksize + guardsize; - /* Use MAP_NORESERVE so that RAM will not be wasted on the guard - bands; touch all the pages of the actual stack before returning, - so we know they are allocated. */ - desc->alloc_base = xmmap (0, - desc->alloc_size, - PROT_READ|PROT_WRITE, - MAP_PRIVATE|MAP_ANONYMOUS|MAP_NORESERVE|MAP_STACK, - -1); - - xmprotect (desc->alloc_base, guardsize, PROT_NONE); - xmprotect (desc->alloc_base + guardsize + stacksize, guardsize, PROT_NONE); - memset (desc->alloc_base + guardsize, 0xA5, stacksize); - - desc->alt_stack.ss_sp = desc->alloc_base + guardsize; + desc->stack = support_stack_alloc (size); + desc->alt_stack.ss_sp = desc->stack.stack; desc->alt_stack.ss_flags = 0; - desc->alt_stack.ss_size = stacksize; + desc->alt_stack.ss_size = desc->stack.size; if (sigaltstack (&desc->alt_stack, &desc->old_stack)) FAIL_EXIT1 ("sigaltstack (new stack: sp=%p, size=%zu, flags=%u): %m\n", @@ -101,7 +68,7 @@ xfree_sigstack (void *stack) FAIL_EXIT1 ("sigaltstack (restore old stack: sp=%p, size=%zu, flags=%u): " "%m\n", desc->old_stack.ss_sp, desc->old_stack.ss_size, desc->old_stack.ss_flags); - xmunmap (desc->alloc_base, desc->alloc_size); + support_stack_free (&desc->stack); free (desc); } |