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oslib: allocate PROT_NONE pages on top of RAM 

This inserts a read and write protected page between RAM and QEMU
memory. This makes it harder to exploit QEMU bugs resulting from buffer
overflows in devices using variants of cpu_physical_memory_map,
dma_memory_map etc.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Michael S. Tsirkin 2015-09-10 16:41:17 +03:00
parent c2dfc5ba3f
commit 9fac18f03a
1 changed files with 4 additions and 4 deletions
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8
util/oslib-posix.c
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@ -128,7 +128,7 @@ void *qemu_memalign(size_t alignment, size_t size)
void *qemu_anon_ram_alloc(size_t size, uint64_t *alignment)
{
size_t align = QEMU_VMALLOC_ALIGN;
size_t total = size + align - getpagesize();
size_t total = size + align;
void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
size_t offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;
void *ptr1;
@ -154,8 +154,8 @@ void *qemu_anon_ram_alloc(size_t size, uint64_t *alignment)
if (offset > 0) {
munmap(ptr - offset, offset);
}
if (total > size) {
munmap(ptr + size, total - size);
if (total > size + getpagesize()) {
munmap(ptr + size + getpagesize(), total - size - getpagesize());
}
trace_qemu_anon_ram_alloc(size, ptr);
@ -172,7 +172,7 @@ void qemu_anon_ram_free(void *ptr, size_t size)
{
trace_qemu_anon_ram_free(ptr, size);
if (ptr) {
munmap(ptr, size);
munmap(ptr, size + getpagesize());
}
}