bpf: Support doubleword alignment in bpf_jit_binary_alloc (b7b3fc8d) · Commits · 戴 / test

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> Signed-off-by:

Daniel Borkmann <daniel@iogearbox.net> Link: https://lore.kernel.org/bpf/20191115123722.58462-1-iii@linux.ibm.com

include/linux/filter.h

+4 −2

Original line number	Diff line number	Diff line
		@@ -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 {

kernel/bpf/core.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -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.

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