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bpf: Support doubleword alignment in bpf_jit_binary_alloc

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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
This commit is contained in:
Ilya Leoshkevich 2019-11-15 13:37:22 +01:00 committed by Daniel Borkmann
parent e47a179997
commit b7b3fc8dd9
2 changed files with 8 additions and 2 deletions
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6
include/linux/filter.h
View file

@ -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 {

4
kernel/bpf/core.c
View file

@ -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.