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e23bb04b0c
If BTF data is missing or removed from the ELF section it is still exported
via sysfs as a zero-length file:
root@OpenWrt:/# ls -l /sys/kernel/btf/vmlinux
-r--r--r-- 1 root root 0 Jul 18 02:59 /sys/kernel/btf/vmlinux
Moreover, reads from this file succeed and leak kernel data:
root@OpenWrt:/# hexdump -C /sys/kernel/btf/vmlinux|head -10
000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
000cc0 00 00 00 00 00 00 00 00 00 00 00 00 80 83 b0 80 |................|
000cd0 00 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000ce0 00 00 00 00 00 00 00 00 00 00 00 00 57 ac 6e 9d |............W.n.|
000cf0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
002650 00 00 00 00 00 00 00 10 00 00 00 01 00 00 00 01 |................|
002660 80 82 9a c4 80 85 97 80 81 a9 51 68 00 00 00 02 |..........Qh....|
002670 80 25 44 dc 80 85 97 80 81 a9 50 24 81 ab c4 60 |.%D.......P$...`|
This situation was first observed with kernel 5.4.x, cross-compiled for a
MIPS target system. Fix by adding a sanity-check for export of zero-length
data sections.
Fixes: 341dfcf8d7 ("btf: expose BTF info through sysfs")
Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/b38db205a66238f70823039a8c531535864eaac5.1600417359.git.Tony.Ambardar@gmail.com
45 lines
1.1 KiB
C
45 lines
1.1 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Provide kernel BTF information for introspection and use by eBPF tools.
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/kobject.h>
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#include <linux/init.h>
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#include <linux/sysfs.h>
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/* See scripts/link-vmlinux.sh, gen_btf() func for details */
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extern char __weak __start_BTF[];
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extern char __weak __stop_BTF[];
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static ssize_t
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btf_vmlinux_read(struct file *file, struct kobject *kobj,
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struct bin_attribute *bin_attr,
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char *buf, loff_t off, size_t len)
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{
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memcpy(buf, __start_BTF + off, len);
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return len;
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}
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static struct bin_attribute bin_attr_btf_vmlinux __ro_after_init = {
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.attr = { .name = "vmlinux", .mode = 0444, },
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.read = btf_vmlinux_read,
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};
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static struct kobject *btf_kobj;
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static int __init btf_vmlinux_init(void)
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{
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bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF;
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if (!__start_BTF || bin_attr_btf_vmlinux.size == 0)
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return 0;
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btf_kobj = kobject_create_and_add("btf", kernel_kobj);
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if (!btf_kobj)
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return -ENOMEM;
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return sysfs_create_bin_file(btf_kobj, &bin_attr_btf_vmlinux);
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}
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subsys_initcall(btf_vmlinux_init);
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