[PATCH] parisc: fix unaligned accesses in BPF

[PATCH] parisc: fix unaligned accesses in BPF

[Mikulas Patocka]

There were spurious unaligned access warnings when calling BPF code.
Sometimes, the warnings were triggered with any incoming packet, making
the machine hard to use.

The reason for the warnings is this: on parisc64, pointers to functions
are not really pointers to functions, they are pointers to 16-byte
descriptor. The first 8 bytes of the descriptor is a pointer to the
function and the next 8 bytes of the descriptor is the content of the
"dp" register. This descriptor is generated in the function
bpf_jit_build_prologue.

The problem is that the function bpf_int_jit_compile advertises 4-byte
alignment when calling bpf_jit_binary_alloc, bpf_jit_binary_alloc
randomizes the returned array and if the array happens to be not aligned
on 8-byte boundary, the descriptor generated in bpf_jit_build_prologue is
also not aligned and this triggers the unaligned access warning.

Fix this by advertising 8-byte alignment on parisc64 when calling
bpf_jit_binary_alloc.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org

---
 arch/parisc/net/bpf_jit_core.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-6.10/arch/parisc/net/bpf_jit_core.c
===================================================================
--- linux-6.10.orig/arch/parisc/net/bpf_jit_core.c	2024-07-23 20:35:34.000000000 +0200
+++ linux-6.10/arch/parisc/net/bpf_jit_core.c	2024-07-27 11:40:17.000000000 +0200
@@ -114,7 +114,7 @@ struct bpf_prog *bpf_int_jit_compile(str
 			jit_data->header =
 				bpf_jit_binary_alloc(prog_size + extable_size,
 						     &jit_data->image,
-						     sizeof(u32),
+						     sizeof(long),
 						     bpf_fill_ill_insns);
 			if (!jit_data->header) {
 				prog = orig_prog;

Re: [PATCH] parisc: fix unaligned accesses in BPF

[Helge Deller]

On 7/27/24 12:11, Mikulas Patocka wrote:
> There were spurious unaligned access warnings when calling BPF code.
> Sometimes, the warnings were triggered with any incoming packet, making
> the machine hard to use.
>
> The reason for the warnings is this: on parisc64, pointers to functions
> are not really pointers to functions, they are pointers to 16-byte
> descriptor. The first 8 bytes of the descriptor is a pointer to the
> function and the next 8 bytes of the descriptor is the content of the
> "dp" register. This descriptor is generated in the function
> bpf_jit_build_prologue.
>
> The problem is that the function bpf_int_jit_compile advertises 4-byte
> alignment when calling bpf_jit_binary_alloc, bpf_jit_binary_alloc
> randomizes the returned array and if the array happens to be not aligned
> on 8-byte boundary, the descriptor generated in bpf_jit_build_prologue is
> also not aligned and this triggers the unaligned access warning.
>
> Fix this by advertising 8-byte alignment on parisc64 when calling
> bpf_jit_binary_alloc.
>
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> Cc: stable@vger.kernel.org

Nice catch!
Applied.

Thanks!
Helge

>
> ---
>   arch/parisc/net/bpf_jit_core.c |    2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> Index: linux-6.10/arch/parisc/net/bpf_jit_core.c
> ===================================================================
> --- linux-6.10.orig/arch/parisc/net/bpf_jit_core.c	2024-07-23 20:35:34.000000000 +0200
> +++ linux-6.10/arch/parisc/net/bpf_jit_core.c	2024-07-27 11:40:17.000000000 +0200
> @@ -114,7 +114,7 @@ struct bpf_prog *bpf_int_jit_compile(str
>   			jit_data->header =
>   				bpf_jit_binary_alloc(prog_size + extable_size,
>   						     &jit_data->image,
> -						     sizeof(u32),
> +						     sizeof(long),
>   						     bpf_fill_ill_insns);
>   			if (!jit_data->header) {
>   				prog = orig_prog;
>