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support: Add support_stack_alloc

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The code to allocate a stack from xsigstack is refactored so it can
be more generic.  The new support_stack_alloc() also set PROT_EXEC
if DEFAULT_STACK_PERMS has PF_X.  This is required on some
 architectures (hppa for instance) and trying to access the rtld
global from testsuite will require more intrusive refactoring
in the ldsodefs.h header.

Checked on x86_64-linux-gnu and i686-linux-gnu.  I also ran
tst-xsigstack on both hppa and ia64.
This commit is contained in:
Adhemerval Zanella
2021-03-10 12:26:29 -03:00
parent 79969f41a7
commit ae8c243d24
4 changed files with 107 additions and 38 deletions
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43
support/xsigstack.c
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@@ -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);
}