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[master] a50db76fa Grossly hack the (debug only) persistent stevedore to cope with ASLR
commit a50db76fa6c5f8092a1a7f0a63a2a8860ec81e8c
Author: Poul-Henning Kamp <phk@FreeBSD.org>
Date: Wed May 4 07:06:48 2022 +0000

Grossly hack the (debug only) persistent stevedore to cope with ASLR

diff --git a/bin/varnishd/storage/mgt_storage_persistent.c b/bin/varnishd/storage/mgt_storage_persistent.c
index 77e8049a2..22c58ab19 100644
--- a/bin/varnishd/storage/mgt_storage_persistent.c
+++ b/bin/varnishd/storage/mgt_storage_persistent.c
@@ -143,7 +143,8 @@ smp_mgt_init(struct stevedore *parent, int ac, char * const *av)
struct smp_sc *sc;
struct smp_sign sgn;
void *target;
- int i;
+ int i, mmap_flags;
+ uintptr_t up;

ASSERT_MGT();

@@ -205,12 +206,38 @@ smp_mgt_init(struct stevedore *parent, int ac, char * const *av)
else
target = NULL;

+ mmap_flags = MAP_NOCORE | MAP_NOSYNC | MAP_SHARED;
+ if (target) {
+ mmap_flags |= MAP_FIXED;
+#ifdef MAP_EXCL
+ mmap_flags |= MAP_EXCL;
+#endif
+ } else {
+ /*
+ * I guess the people who came up with ASLR never learned
+ * that virtual memory can have benficial uses, because they
+ * added no facility for realiably and portably allocing
+ * stable address-space.
+ * This stevedore is only for testing these days, so we
+ * can get away with just hacking something up: 16M below
+ * the break seems to work on FreeBSD.
+ */
+ up = (uintptr_t)sbrk(0);
+ up -= 1ULL<<24;
+ up -= sc->mediasize;
+ up &= ~(getpagesize() - 1ULL);
+ target = (void *)up;
+
+#ifdef MAP_ALIGNED_SUPER
+ mmap_flags |= MAP_ALIGNED_SUPER;
+#endif
+ }
sc->base = (void*)mmap(target, sc->mediasize, PROT_READ|PROT_WRITE,
- MAP_NOCORE | MAP_NOSYNC | MAP_SHARED, sc->fd, 0);
+ mmap_flags, sc->fd, 0);

if (sc->base == MAP_FAILED)
- ARGV_ERR("(-spersistent) failed to mmap (%s)\n",
- VAS_errtxt(errno));
+ ARGV_ERR("(-spersistent) failed to mmap (%s) @%p\n",
+ VAS_errtxt(errno), target);
if (target != NULL && sc->base != target)
fprintf(stderr, "WARNING: Persistent silo lost to ASLR %s\n",
sc->filename);
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