Re: [PATCH bpf-next v3 2/2] bpf: Check return from set_memory_rox()

[Kui-Feng Lee <sinquersw@gmail.com>]

On 3/15/24 10:06, Christophe Leroy wrote:
> arch_protect_bpf_trampoline() and alloc_new_pack() call
> set_memory_rox() which can fail, leading to unprotected memory.
> 
> Take into account return from set_memory_rox() function and add
> __must_check flag to arch_protect_bpf_trampoline().
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> ---
> v3:
> - Rebased and handled conflict in kernel/bpf/bpf_struct_ops.c
> 
> v2:
> - Move list_add_tail(&pack->list, &pack_list) at the end of alloc_new_pack()
> - Split 2 lines that are reported longer than 80 chars by BPF patchwork's checkpatch report.
> ---
>   arch/arm64/net/bpf_jit_comp.c  |  3 ++-
>   arch/x86/net/bpf_jit_comp.c    |  3 ++-
>   include/linux/bpf.h            |  2 +-
>   kernel/bpf/bpf_struct_ops.c    |  7 +++++--
>   kernel/bpf/core.c              | 29 ++++++++++++++++++++++-------
>   kernel/bpf/trampoline.c        |  8 +++++---
>   net/bpf/bpf_dummy_struct_ops.c |  4 +++-
>   7 files changed, 40 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
> index 132c8ffba109..bc16eb694657 100644
> --- a/arch/arm64/net/bpf_jit_comp.c
> +++ b/arch/arm64/net/bpf_jit_comp.c
> @@ -2176,8 +2176,9 @@ void arch_free_bpf_trampoline(void *image, unsigned int size)
>   	bpf_prog_pack_free(image, size);
>   }
>   
> -void arch_protect_bpf_trampoline(void *image, unsigned int size)
> +int arch_protect_bpf_trampoline(void *image, unsigned int size)
>   {
> +	return 0;
>   }
>   
>   int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *ro_image,
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 7a56d2d84512..4900b1ee019f 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -3004,8 +3004,9 @@ void arch_free_bpf_trampoline(void *image, unsigned int size)
>   	bpf_prog_pack_free(image, size);
>   }
>   
> -void arch_protect_bpf_trampoline(void *image, unsigned int size)
> +int arch_protect_bpf_trampoline(void *image, unsigned int size)
>   {
> +	return 0;
>   }
>   
>   int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *image_end,
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index d89bdefb42e2..17843e66a1d3 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1116,7 +1116,7 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
>   				void *func_addr);
>   void *arch_alloc_bpf_trampoline(unsigned int size);
>   void arch_free_bpf_trampoline(void *image, unsigned int size);
> -void arch_protect_bpf_trampoline(void *image, unsigned int size);
> +int __must_check arch_protect_bpf_trampoline(void *image, unsigned int size);
>   int arch_bpf_trampoline_size(const struct btf_func_model *m, u32 flags,
>   			     struct bpf_tramp_links *tlinks, void *func_addr);
>   
> diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
> index 43356faaa057..ca1d9b87c475 100644
> --- a/kernel/bpf/bpf_struct_ops.c
> +++ b/kernel/bpf/bpf_struct_ops.c
> @@ -742,8 +742,11 @@ static long bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
>   		if (err)
>   			goto reset_unlock;
>   	}
> -	for (i = 0; i < st_map->image_pages_cnt; i++)
> -		arch_protect_bpf_trampoline(st_map->image_pages[i], PAGE_SIZE);
> +	for (i = 0; i < st_map->image_pages_cnt && !err; i++)
> +		err = arch_protect_bpf_trampoline(st_map->image_pages[i], PAGE_SIZE);
> +
> +	if (err)

nit: Can it be more specific? I mean to check err < 0, so we can reason
that this function never returns a positive value other than 0.

> +		goto reset_unlock;
>   
>   	if (st_map->map.map_flags & BPF_F_LINK) {
>   		err = 0;
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 63f100def31b..1e761c3c66db 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -908,23 +908,31 @@ static LIST_HEAD(pack_list);
>   static struct bpf_prog_pack *alloc_new_pack(bpf_jit_fill_hole_t bpf_fill_ill_insns)
>   {
>   	struct bpf_prog_pack *pack;
> +	int err;
>   
>   	pack = kzalloc(struct_size(pack, bitmap, BITS_TO_LONGS(BPF_PROG_CHUNK_COUNT)),
>   		       GFP_KERNEL);
>   	if (!pack)
>   		return NULL;
>   	pack->ptr = bpf_jit_alloc_exec(BPF_PROG_PACK_SIZE);
> -	if (!pack->ptr) {
> -		kfree(pack);
> -		return NULL;
> -	}
> +	if (!pack->ptr)
> +		goto out;
>   	bpf_fill_ill_insns(pack->ptr, BPF_PROG_PACK_SIZE);
>   	bitmap_zero(pack->bitmap, BPF_PROG_PACK_SIZE / BPF_PROG_CHUNK_SIZE);
> -	list_add_tail(&pack->list, &pack_list);
>   
>   	set_vm_flush_reset_perms(pack->ptr);
> -	set_memory_rox((unsigned long)pack->ptr, BPF_PROG_PACK_SIZE / PAGE_SIZE);
> +	err = set_memory_rox((unsigned long)pack->ptr,
> +			     BPF_PROG_PACK_SIZE / PAGE_SIZE);
> +	if (err)
> +		goto out_free;
> +	list_add_tail(&pack->list, &pack_list);
>   	return pack;
> +
> +out_free:
> +	bpf_jit_free_exec(pack->ptr);
> +out:
> +	kfree(pack);
> +	return NULL;
>   }
>   
>   void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insns)
> @@ -939,9 +947,16 @@ void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insns)
>   		size = round_up(size, PAGE_SIZE);
>   		ptr = bpf_jit_alloc_exec(size);
>   		if (ptr) {
> +			int err;
> +
>   			bpf_fill_ill_insns(ptr, size);
>   			set_vm_flush_reset_perms(ptr);
> -			set_memory_rox((unsigned long)ptr, size / PAGE_SIZE);
> +			err = set_memory_rox((unsigned long)ptr,
> +					     size / PAGE_SIZE);
> +			if (err) {
> +				bpf_jit_free_exec(ptr);
> +				ptr = NULL;
> +			}
>   		}
>   		goto out;
>   	}
> diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
> index 04fd1abd3661..cc50607f8d8c 100644
> --- a/kernel/bpf/trampoline.c
> +++ b/kernel/bpf/trampoline.c
> @@ -456,7 +456,9 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
>   	if (err < 0)
>   		goto out_free;

Same here

>   
> -	arch_protect_bpf_trampoline(im->image, im->size);
> +	err = arch_protect_bpf_trampoline(im->image, im->size);
> +	if (err)
> +		goto out_free;
>   
>   	WARN_ON(tr->cur_image && total == 0);
>   	if (tr->cur_image)
> @@ -1072,10 +1074,10 @@ void __weak arch_free_bpf_trampoline(void *image, unsigned int size)
>   	bpf_jit_free_exec(image);
>   }
>   
> -void __weak arch_protect_bpf_trampoline(void *image, unsigned int size)
> +int __weak arch_protect_bpf_trampoline(void *image, unsigned int size)
>   {
>   	WARN_ON_ONCE(size > PAGE_SIZE);
> -	set_memory_rox((long)image, 1);
> +	return set_memory_rox((long)image, 1);
>   }
>   
>   int __weak arch_bpf_trampoline_size(const struct btf_func_model *m, u32 flags,
> diff --git a/net/bpf/bpf_dummy_struct_ops.c b/net/bpf/bpf_dummy_struct_ops.c
> index de33dc1b0daa..25b75844891a 100644
> --- a/net/bpf/bpf_dummy_struct_ops.c
> +++ b/net/bpf/bpf_dummy_struct_ops.c
> @@ -133,7 +133,9 @@ int bpf_struct_ops_test_run(struct bpf_prog *prog, const union bpf_attr *kattr,
>   	if (err < 0)
>   		goto out;
>   
> -	arch_protect_bpf_trampoline(image, PAGE_SIZE);
> +	err = arch_protect_bpf_trampoline(image, PAGE_SIZE);
> +	if (err)

Same here.

> +		goto out;
>   	prog_ret = dummy_ops_call_op(image, args);
>   
>   	err = dummy_ops_copy_args(args);