diff mbox series

[mm,v3,31/38] kasan, arm64: don't tag executable vmalloc allocations

Message ID 4a5ec956a2666c1f967c9789534a8ac4d4fe26f9.1639432170.git.andreyknvl@google.com (mailing list archive)
State New
Headers show
Series kasan, vmalloc, arm64: add vmalloc tagging support for SW/HW_TAGS | expand

Commit Message

andrey.konovalov@linux.dev Dec. 13, 2021, 9:54 p.m. UTC 
From: Andrey Konovalov <andreyknvl@google.com>

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().

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

---

Changes v2->v3:
- Add this patch.
---
 arch/arm64/kernel/module.c    | 3 ++-
 arch/arm64/net/bpf_jit_comp.c | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

Comments

Andrey Konovalov Dec. 13, 2021, 9:59 p.m. UTC | #1 
On Mon, Dec 13, 2021 at 10:55 PM <andrey.konovalov@linux.dev> wrote:
>
> From: Andrey Konovalov <andreyknvl@google.com>
>
> 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().
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
>
> ---
>
> Changes v2->v3:
> - Add this patch.
> ---
>  arch/arm64/kernel/module.c    | 3 ++-
>  arch/arm64/net/bpf_jit_comp.c | 3 ++-
>  2 files changed, 4 insertions(+), 2 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/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
>

Catalin, Vincenzo,

This is a new patch added in v3. Could you PTAL? Thanks!
Catalin Marinas Dec. 17, 2021, 1:45 p.m. UTC | #2 
On Mon, Dec 13, 2021 at 10:54:27PM +0100, andrey.konovalov@linux.dev wrote:
> From: Andrey Konovalov <andreyknvl@google.com>
> 
> 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().
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
diff mbox series

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/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)