| Message ID | 20191115123722.58462-1-iii@linux.ibm.com |
|---|---|
| State | Accepted |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | [bpf-next,v2] bpf: support doubleword alignment in bpf_jit_binary_alloc | expand |
On 11/15/19 1:37 PM, Ilya Leoshkevich wrote: > Currently passing alignment greater than 4 to bpf_jit_binary_alloc does > not work: in such cases it silently aligns only to 4 bytes. > > On s390, in order to load a constant from memory in a large (>512k) BPF > program, one must use lgrl instruction, whose memory operand must be > aligned on an 8-byte boundary. > > This patch makes it possible to request 8-byte alignment from > bpf_jit_binary_alloc, and also makes it issue a warning when an > unsupported alignment is requested. > > Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com> Applied, thanks!
diff --git a/include/linux/filter.h b/include/linux/filter.h index 7a6f8f6f1da4..ad80e9c6111c 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -515,10 +515,12 @@ struct sock_fprog_kern { struct sock_filter *filter; }; +/* Some arches need doubleword alignment for their instructions and/or data */ +#define BPF_IMAGE_ALIGNMENT 8 + struct bpf_binary_header { u32 pages; - /* Some arches need word alignment for their instructions */ - u8 image[] __aligned(4); + u8 image[] __aligned(BPF_IMAGE_ALIGNMENT); }; struct bpf_prog { diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index c1fde0303280..99693f3c4e99 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -31,6 +31,7 @@ #include <linux/rcupdate.h> #include <linux/perf_event.h> #include <linux/extable.h> +#include <linux/log2.h> #include <asm/unaligned.h> /* Registers */ @@ -815,6 +816,9 @@ bpf_jit_binary_alloc(unsigned int proglen, u8 **image_ptr, struct bpf_binary_header *hdr; u32 size, hole, start, pages; + WARN_ON_ONCE(!is_power_of_2(alignment) || + alignment > BPF_IMAGE_ALIGNMENT); + /* Most of BPF filters are really small, but if some of them * fill a page, allow at least 128 extra bytes to insert a * random section of illegal instructions.
Currently passing alignment greater than 4 to bpf_jit_binary_alloc does not work: in such cases it silently aligns only to 4 bytes. On s390, in order to load a constant from memory in a large (>512k) BPF program, one must use lgrl instruction, whose memory operand must be aligned on an 8-byte boundary. This patch makes it possible to request 8-byte alignment from bpf_jit_binary_alloc, and also makes it issue a warning when an unsupported alignment is requested. Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com> --- v1 -> v2: Simply bump alignment to 8, don't try to be too generic. include/linux/filter.h | 6 ++++-- kernel/bpf/core.c | 4 ++++ 2 files changed, 8 insertions(+), 2 deletions(-)