Date: Mon, 04 May 2026 17:28:21 +0000 From: Mark Johnston <markj@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: eca4dd133883 - main - execve: Add guard pages around execve KVA buffers Message-ID: <69f8d735.30a39.330b25c8@gitrepo.freebsd.org>
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The branch main has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=eca4dd133883c9e9aaeca68e0119a638ba0aaca7 commit eca4dd133883c9e9aaeca68e0119a638ba0aaca7 Author: Mark Johnston <markj@FreeBSD.org> AuthorDate: 2026-05-04 15:38:54 +0000 Commit: Mark Johnston <markj@FreeBSD.org> CommitDate: 2026-05-04 17:28:02 +0000 execve: Add guard pages around execve KVA buffers This helps ensure that overflows will trigger a panic instead of silently corrupting adjacent buffers, as happened in SA-26:13.exec. Extend kmap_alloc_wait() to support allocation of guard pages on both sides of a KVA allocation. Modify the exec_map setup accordingly. Add the "vm.exec_map_guard_pages" tunable to provide control over the guard page allocations. Reviewed by: kib MFC after: 2 weeks Differential Revision: https://reviews.freebsd.org/D56711 --- sys/kern/kern_exec.c | 3 ++- sys/vm/vm_extern.h | 2 +- sys/vm/vm_init.c | 8 ++++++-- sys/vm/vm_kern.c | 39 ++++++++++++++++++++++++++++++++------- sys/vm/vm_kern.h | 1 + 5 files changed, 42 insertions(+), 11 deletions(-) diff --git a/sys/kern/kern_exec.c b/sys/kern/kern_exec.c index 8e3b41170cab..958ec559fd8d 100644 --- a/sys/kern/kern_exec.c +++ b/sys/kern/kern_exec.c @@ -1435,7 +1435,8 @@ exec_prealloc_args_kva(void *arg __unused) mtx_init(&exec_args_kva_mtx, "exec args kva", NULL, MTX_DEF); for (i = 0; i < exec_map_entries; i++) { argkva = malloc(sizeof(*argkva), M_PARGS, M_WAITOK); - argkva->addr = kmap_alloc_wait(exec_map, exec_map_entry_size); + argkva->addr = kmap_alloc_wait(exec_map, exec_map_entry_size, + ptoa(exec_map_guard_pages)); argkva->gen = exec_args_gen; SLIST_INSERT_HEAD(&exec_args_kva_freelist, argkva, next); } diff --git a/sys/vm/vm_extern.h b/sys/vm/vm_extern.h index 207eb721d129..799b89ce2fc8 100644 --- a/sys/vm/vm_extern.h +++ b/sys/vm/vm_extern.h @@ -51,7 +51,7 @@ void *kva_alloc_aligned(vm_size_t, vm_size_t); void kva_free(void *, vm_size_t); /* These operate on pageable virtual addresses. */ -void *kmap_alloc_wait(vm_map_t, vm_size_t); +void *kmap_alloc_wait(vm_map_t, vm_size_t, vm_size_t); void kmap_free_wakeup(vm_map_t, void *, vm_size_t); /* These operate on virtual addresses backed by memory. */ diff --git a/sys/vm/vm_init.c b/sys/vm/vm_init.c index 40a001afb300..316b43c1c240 100644 --- a/sys/vm/vm_init.c +++ b/sys/vm/vm_init.c @@ -274,8 +274,12 @@ again: exec_map_entries = 2 * mp_ncpus + 4; #endif exec_map_entry_size = round_page(PATH_MAX + ARG_MAX); - kmem_subinit(exec_map, kernel_map, &minaddr, &maxaddr, - exec_map_entries * exec_map_entry_size + 64 * PAGE_SIZE, false); + exec_map_guard_pages = 1; + TUNABLE_INT_FETCH("vm.exec_map_guard_pages", &exec_map_guard_pages); + size = exec_map_entries * + (exec_map_entry_size + 2 * ptoa(exec_map_guard_pages)) + + 64 * PAGE_SIZE; + kmem_subinit(exec_map, kernel_map, &minaddr, &maxaddr, size, false); kmem_subinit(pipe_map, kernel_map, &minaddr, &maxaddr, maxpipekva, false); TSEXIT(); diff --git a/sys/vm/vm_kern.c b/sys/vm/vm_kern.c index 3a6fed6cb3e1..fc5d0de424bd 100644 --- a/sys/vm/vm_kern.c +++ b/sys/vm/vm_kern.c @@ -107,6 +107,7 @@ CTASSERT((ZERO_REGION_SIZE & PAGE_MASK) == 0); const u_long vm_maxuser_address = VM_MAXUSER_ADDRESS; u_int exec_map_entry_size; +u_int exec_map_guard_pages; u_int exec_map_entries; SYSCTL_ULONG(_vm, OID_AUTO, min_kernel_address, CTLFLAG_RD, @@ -706,34 +707,52 @@ kmem_free(void *addr, vm_size_t size) vmem_free(arena, (uintptr_t)addr, size); } +static void +kmap_alloc_map(vm_map_t map, vm_offset_t addr, vm_size_t size, + vm_prot_t prot, int flags) +{ + int error __diagused; + + error = vm_map_insert(map, NULL, 0, + addr, addr + size, prot, prot, flags); + KASSERT(error == KERN_SUCCESS, + ("%s: unexpected error %d", __func__, error)); +} + /* * kmap_alloc_wait: * * Allocates pageable memory from a sub-map of the kernel. If the submap * has no room, the caller sleeps waiting for more memory in the submap. + * If "guard_size" is non-zero, then unmapped KVA is left at the beginning + * and end of the allocated range. * * This routine may block. */ void * -kmap_alloc_wait(vm_map_t map, vm_size_t size) +kmap_alloc_wait(vm_map_t map, vm_size_t size, vm_size_t guard_size) { vm_offset_t addr; + vm_size_t total_size; + + KASSERT(size % PAGE_SIZE == 0 && guard_size % PAGE_SIZE == 0, + ("%s: size %zu guard_size %zu", __func__, size, guard_size)); - size = round_page(size); if (!swap_reserve(size)) return (NULL); + total_size = size + 2 * guard_size; for (;;) { /* * To make this work for more than one map, use the map's lock * to lock out sleepers/wakers. */ vm_map_lock(map); - addr = vm_map_findspace(map, vm_map_min(map), size); - if (addr + size <= vm_map_max(map)) + addr = vm_map_findspace(map, vm_map_min(map), total_size); + if (addr + total_size <= vm_map_max(map)) break; /* no space now; see if we can ever get space */ - if (vm_map_max(map) - vm_map_min(map) < size) { + if (vm_map_max(map) - vm_map_min(map) < total_size) { vm_map_unlock(map); swap_release(size); return (0); @@ -741,10 +760,16 @@ kmap_alloc_wait(vm_map_t map, vm_size_t size) vm_map_modflags(map, MAP_NEEDS_WAKEUP, 0); vm_map_unlock_and_wait(map, 0); } - vm_map_insert(map, NULL, 0, addr, addr + size, VM_PROT_RW, VM_PROT_RW, + if (guard_size != 0) { + kmap_alloc_map(map, addr, guard_size, + VM_PROT_NONE, MAP_CREATE_GUARD); + kmap_alloc_map(map, addr + guard_size + size, guard_size, + VM_PROT_NONE, MAP_CREATE_GUARD); + } + kmap_alloc_map(map, addr + guard_size, size, VM_PROT_RW, MAP_ACC_CHARGED); vm_map_unlock(map); - return ((void *)addr); + return ((void *)(addr + guard_size)); } /* diff --git a/sys/vm/vm_kern.h b/sys/vm/vm_kern.h index 942c03480364..296a50ae0058 100644 --- a/sys/vm/vm_kern.h +++ b/sys/vm/vm_kern.h @@ -75,4 +75,5 @@ extern struct vmem *memguard_arena; extern u_long vm_kmem_size; extern u_int exec_map_entries; extern u_int exec_map_entry_size; +extern u_int exec_map_guard_pages; #endif /* _VM_VM_KERN_H_ */home | help
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