[PATCH mm v4 32/39] kasan, arm64: don't tag executable vmalloc allocations

andrey.konovalov
2021-12-20T22:02:33Z

Besides asking vmalloc memory to be executable via the prot argument
of __vmalloc_node_range() (see the previous patch), the kernel can skip
that bit and instead mark memory as executable via set_memory_x().

Once tag-based KASAN modes start tagging vmalloc allocations, executing
code from such allocations will lead to the PC register getting a tag,
which is not tolerated by the kernel.

Generic kernel code typically allocates memory via module_alloc() if
it intends to mark memory as executable. (On arm64 module_alloc()
uses __vmalloc_node_range() without setting the executable bit).

Thus, reset pointer tags of pointers returned from module_alloc().

However, on arm64 there's an exception: the eBPF subsystem. Instead of
using module_alloc(), it uses vmalloc() (via bpf_jit_alloc_exec())
to allocate its JIT region.

Thus, reset pointer tags of pointers returned from bpf_jit_alloc_exec().

Resetting tags for these pointers results in untagged pointers being
passed to set_memory_x(). This causes conflicts in arithmetic checks
in change_memory_common(), as vm_struct->addr pointer returned by
find_vm_area() is tagged.

Reset pointer tag of find_vm_area(addr)->addr in change_memory_common().

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

---

Changes v3->v4:
- Reset pointer tag in change_memory_common().

Changes v2->v3:
- Add this patch.
---
arch/arm64/kernel/module.c | 3 ++-
arch/arm64/mm/pageattr.c | 2 +-
arch/arm64/net/bpf_jit_comp.c | 3 ++-
3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c
index d3a1fa818348..f2d4bb14bfab 100644
--- a/arch/arm64/kernel/module.c
+++ b/arch/arm64/kernel/module.c
@@ -63,7 +63,8 @@ void *module_alloc(unsigned long size)
return NULL;
}

- return p;
+ /* Memory is intended to be executable, reset the pointer tag. */
+ return kasan_reset_tag(p);
}

enum aarch64_reloc_op {
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index a3bacd79507a..64e985eaa52d 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -85,7 +85,7 @@ static int change_memory_common(unsigned long addr, int numpages,
*/
area = find_vm_area((void *)addr);
if (!area ||
- end > (unsigned long)area->addr + area->size ||
+ end > (unsigned long)kasan_reset_tag(area->addr) + area->size ||
!(area->flags & VM_ALLOC))
return -EINVAL;

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index 07aad85848fa..381a67922c2d 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -1147,7 +1147,8 @@ u64 bpf_jit_alloc_exec_limit(void)

void *bpf_jit_alloc_exec(unsigned long size)
{
- return vmalloc(size);
+ /* Memory is intended to be executable, reset the pointer tag. */
+ return kasan_reset_tag(vmalloc(size));
}

void bpf_jit_free_exec(void *addr)
--
2.25.1