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

Commit Message

[e-mail] Dec. 20, 2021, 10:02 p.m. UTC

From: Andrey Konovalov <[e-mail]>

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 <[e-mail]>

---

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(-)

Comments

Andrey Konovalov Dec. 20, 2021, 10:05 p.m. UTC | #1

On Mon, Dec 20, 2021 at 11:02 PM <[e-mail]> wrote:
>
> From: Andrey Konovalov <[e-mail]>
>
> 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 <[e-mail]>
>
> ---
>
> 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

Hi Catalin,

I had to change this patch to fix an issue I discovered during
testing. Could you PTAL once again?

Thanks!

Catalin Marinas Dec. 22, 2021, 11:11 a.m. UTC | #2

On Mon, Dec 20, 2021 at 11:02:04PM +0100, [e-mail] wrote:
> From: Andrey Konovalov <[e-mail]>
> 
> 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 <[e-mail]>
> 

Acked-by: Catalin Marinas <[e-mail]>

Patch

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)