From 8f5ca8d21cadd6307af86e46cf86e60f5cca7970 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bj=C3=B6rn=20T=C3=B6pel?= Date: Fri, 13 Dec 2019 18:51:12 +0100 Subject: [PATCH] UPSTREAM: bpf, x86: Align dispatcher branch targets to 16B MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit >From Intel 64 and IA-32 Architectures Optimization Reference Manual, 3.4.1.4 Code Alignment, Assembly/Compiler Coding Rule 11: All branch targets should be 16-byte aligned. This commits aligns branch targets according to the Intel manual. The nops used to align branch targets make the dispatcher larger, and therefore the number of supported dispatch points/programs are descreased from 64 to 48. Signed-off-by: Björn Töpel Signed-off-by: Alexei Starovoitov Link: https://lore.kernel.org/bpf/20191213175112.30208-7-bjorn.topel@gmail.com (cherry picked from commit 116eb788f57c9c35c40b29cfaa2607020de99a84) Bug: 145210207 Change-Id: I04996cd41bf109aaa63b5aa23773c34ef1f90d8b Signed-off-by: Sami Tolvanen --- arch/x86/net/bpf_jit_comp.c | 30 +++++++++++++++++++++++++++++- include/linux/bpf.h | 2 +- 2 files changed, 30 insertions(+), 2 deletions(-) diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 9b2d3e526e05..cd887e8db536 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -1521,6 +1521,26 @@ static int emit_cond_near_jump(u8 **pprog, void *func, void *ip, u8 jmp_cond) return 0; } +static void emit_nops(u8 **pprog, unsigned int len) +{ + unsigned int i, noplen; + u8 *prog = *pprog; + int cnt = 0; + + while (len > 0) { + noplen = len; + + if (noplen > ASM_NOP_MAX) + noplen = ASM_NOP_MAX; + + for (i = 0; i < noplen; i++) + EMIT1(ideal_nops[noplen][i]); + len -= noplen; + } + + *pprog = prog; +} + static int emit_fallback_jump(u8 **pprog) { u8 *prog = *pprog; @@ -1543,8 +1563,8 @@ static int emit_fallback_jump(u8 **pprog) static int emit_bpf_dispatcher(u8 **pprog, int a, int b, s64 *progs) { + u8 *jg_reloc, *jg_target, *prog = *pprog; int pivot, err, jg_bytes = 1, cnt = 0; - u8 *jg_reloc, *prog = *pprog; s64 jg_offset; if (a == b) { @@ -1593,6 +1613,14 @@ static int emit_bpf_dispatcher(u8 **pprog, int a, int b, s64 *progs) if (err) return err; + /* From Intel 64 and IA-32 Architectures Optimization + * Reference Manual, 3.4.1.4 Code Alignment, Assembly/Compiler + * Coding Rule 11: All branch targets should be 16-byte + * aligned. + */ + jg_target = PTR_ALIGN(prog, 16); + if (jg_target != prog) + emit_nops(&prog, jg_target - prog); jg_offset = prog - jg_reloc; emit_code(jg_reloc - jg_bytes, jg_offset, jg_bytes); diff --git a/include/linux/bpf.h b/include/linux/bpf.h index fed7cfa51adb..9d304eeb4a88 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -472,7 +472,7 @@ struct bpf_trampoline { u64 selector; }; -#define BPF_DISPATCHER_MAX 64 /* Fits in 2048B */ +#define BPF_DISPATCHER_MAX 48 /* Fits in 2048B */ struct bpf_dispatcher_prog { struct bpf_prog *prog;