mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2025-01-25 23:34:47 +08:00
b7a0d65d80
With latest llvm compiler, running test_progs will have the following
verifier failure for test_sysctl_loop1.o:
libbpf: load bpf program failed: Permission denied
libbpf: -- BEGIN DUMP LOG ---
libbpf:
invalid indirect read from stack var_off (0x0; 0xff)+196 size 7
...
libbpf: -- END LOG --
libbpf: failed to load program 'cgroup/sysctl'
libbpf: failed to load object 'test_sysctl_loop1.o'
The related bytecode looks as below:
0000000000000308 LBB0_8:
97: r4 = r10
98: r4 += -288
99: r4 += r7
100: w8 &= 255
101: r1 = r10
102: r1 += -488
103: r1 += r8
104: r2 = 7
105: r3 = 0
106: call 106
107: w1 = w0
108: w1 += -1
109: if w1 > 6 goto -24 <LBB0_5>
110: w0 += w8
111: r7 += 8
112: w8 = w0
113: if r7 != 224 goto -17 <LBB0_8>
And source code:
for (i = 0; i < ARRAY_SIZE(tcp_mem); ++i) {
ret = bpf_strtoul(value + off, MAX_ULONG_STR_LEN, 0,
tcp_mem + i);
if (ret <= 0 || ret > MAX_ULONG_STR_LEN)
return 0;
off += ret & MAX_ULONG_STR_LEN;
}
Current verifier is not able to conclude that register w0 before '+'
at insn 110 has a range of 1 to 7 and thinks it is from 0 - 255. This
leads to more conservative range for w8 at insn 112, and later verifier
complaint.
Let us workaround this issue until we found a compiler and/or verifier
solution. The workaround in this patch is to make variable 'ret' volatile,
which will force a reload and then '&' operation to ensure better value
range. With this patch, I got the below byte code for the loop:
0000000000000328 LBB0_9:
101: r4 = r10
102: r4 += -288
103: r4 += r7
104: w8 &= 255
105: r1 = r10
106: r1 += -488
107: r1 += r8
108: r2 = 7
109: r3 = 0
110: call 106
111: *(u32 *)(r10 - 64) = r0
112: r1 = *(u32 *)(r10 - 64)
113: if w1 s< 1 goto -28 <LBB0_5>
114: r1 = *(u32 *)(r10 - 64)
115: if w1 s> 7 goto -30 <LBB0_5>
116: r1 = *(u32 *)(r10 - 64)
117: w1 &= 7
118: w1 += w8
119: r7 += 8
120: w8 = w1
121: if r7 != 224 goto -21 <LBB0_9>
Insn 117 did the '&' operation and we got more precise value range
for 'w8' at insn 120. The test is happy then:
#3/17 test_sysctl_loop1.o:OK
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20191107170045.2503480-1-yhs@fb.com
75 lines
1.8 KiB
C
75 lines
1.8 KiB
C
// SPDX-License-Identifier: GPL-2.0
|
|
// Copyright (c) 2019 Facebook
|
|
|
|
#include <stdint.h>
|
|
#include <string.h>
|
|
|
|
#include <linux/stddef.h>
|
|
#include <linux/bpf.h>
|
|
|
|
#include "bpf_helpers.h"
|
|
|
|
#ifndef ARRAY_SIZE
|
|
#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
|
|
#endif
|
|
|
|
/* tcp_mem sysctl has only 3 ints, but this test is doing TCP_MEM_LOOPS */
|
|
#define TCP_MEM_LOOPS 28 /* because 30 doesn't fit into 512 bytes of stack */
|
|
#define MAX_ULONG_STR_LEN 7
|
|
#define MAX_VALUE_STR_LEN (TCP_MEM_LOOPS * MAX_ULONG_STR_LEN)
|
|
|
|
static __always_inline int is_tcp_mem(struct bpf_sysctl *ctx)
|
|
{
|
|
volatile char tcp_mem_name[] = "net/ipv4/tcp_mem/very_very_very_very_long_pointless_string";
|
|
unsigned char i;
|
|
char name[64];
|
|
int ret;
|
|
|
|
memset(name, 0, sizeof(name));
|
|
ret = bpf_sysctl_get_name(ctx, name, sizeof(name), 0);
|
|
if (ret < 0 || ret != sizeof(tcp_mem_name) - 1)
|
|
return 0;
|
|
|
|
#pragma clang loop unroll(disable)
|
|
for (i = 0; i < sizeof(tcp_mem_name); ++i)
|
|
if (name[i] != tcp_mem_name[i])
|
|
return 0;
|
|
|
|
return 1;
|
|
}
|
|
|
|
SEC("cgroup/sysctl")
|
|
int sysctl_tcp_mem(struct bpf_sysctl *ctx)
|
|
{
|
|
unsigned long tcp_mem[TCP_MEM_LOOPS] = {};
|
|
char value[MAX_VALUE_STR_LEN];
|
|
unsigned char i, off = 0;
|
|
/* a workaround to prevent compiler from generating
|
|
* codes verifier cannot handle yet.
|
|
*/
|
|
volatile int ret;
|
|
|
|
if (ctx->write)
|
|
return 0;
|
|
|
|
if (!is_tcp_mem(ctx))
|
|
return 0;
|
|
|
|
ret = bpf_sysctl_get_current_value(ctx, value, MAX_VALUE_STR_LEN);
|
|
if (ret < 0 || ret >= MAX_VALUE_STR_LEN)
|
|
return 0;
|
|
|
|
#pragma clang loop unroll(disable)
|
|
for (i = 0; i < ARRAY_SIZE(tcp_mem); ++i) {
|
|
ret = bpf_strtoul(value + off, MAX_ULONG_STR_LEN, 0,
|
|
tcp_mem + i);
|
|
if (ret <= 0 || ret > MAX_ULONG_STR_LEN)
|
|
return 0;
|
|
off += ret & MAX_ULONG_STR_LEN;
|
|
}
|
|
|
|
return tcp_mem[0] < tcp_mem[1] && tcp_mem[1] < tcp_mem[2];
|
|
}
|
|
|
|
char _license[] SEC("license") = "GPL";
|