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linux/samples/seccomp/bpf-helper.h
Will Drewry 8ac270d1e2 Documentation: prctl/seccomp_filter 
Documents how system call filtering using Berkeley Packet
Filter programs works and how it may be used.
Includes an example for x86 and a semi-generic
example using a macro-based code generator.

Acked-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Will Drewry <wad@chromium.org>
Acked-by: Kees Cook <keescook@chromium.org>

v18: - added acked by
     - update no new privs numbers
v17: - remove @compat note and add Pitfalls section for arch checking
       (keescook@chromium.org)
v16: -
v15: -
v14: - rebase/nochanges
v13: - rebase on to 88ebdda615
v12: - comment on the ptrace_event use
     - update arch support comment
     - note the behavior of SECCOMP_RET_DATA when there are multiple filters
       (keescook@chromium.org)
     - lots of samples/ clean up incl 64-bit bpf-direct support
       (markus@chromium.org)
     - rebase to linux-next
v11: - overhaul return value language, updates (keescook@chromium.org)
     - comment on do_exit(SIGSYS)
v10: - update for SIGSYS
     - update for new seccomp_data layout
     - update for ptrace option use
v9: - updated bpf-direct.c for SIGILL
v8: - add PR_SET_NO_NEW_PRIVS to the samples.
v7: - updated for all the new stuff in v7: TRAP, TRACE
    - only talk about PR_SET_SECCOMP now
    - fixed bad JLE32 check (coreyb@linux.vnet.ibm.com)
    - adds dropper.c: a simple system call disabler
v6: - tweak the language to note the requirement of
      PR_SET_NO_NEW_PRIVS being called prior to use. (luto@mit.edu)
v5: - update sample to use system call arguments
    - adds a "fancy" example using a macro-based generator
    - cleaned up bpf in the sample
    - update docs to mention arguments
    - fix prctl value (eparis@redhat.com)
    - language cleanup (rdunlap@xenotime.net)
v4: - update for no_new_privs use
    - minor tweaks
v3: - call out BPF <-> Berkeley Packet Filter (rdunlap@xenotime.net)
    - document use of tentative always-unprivileged
    - guard sample compilation for i386 and x86_64
v2: - move code to samples (corbet@lwn.net)
Signed-off-by: James Morris <james.l.morris@oracle.com>
2012-04-14 11:13:22 +10:00

239 lines
7.1 KiB
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/*
* Example wrapper around BPF macros.
*
* Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
* Author: Will Drewry <wad@chromium.org>
*
* The code may be used by anyone for any purpose,
* and can serve as a starting point for developing
* applications using prctl(PR_SET_SECCOMP, 2, ...).
*
* No guarantees are provided with respect to the correctness
* or functionality of this code.
*/
#ifndef __BPF_HELPER_H__
#define __BPF_HELPER_H__
#include <asm/bitsperlong.h> /* for __BITS_PER_LONG */
#include <endian.h>
#include <linux/filter.h>
#include <linux/seccomp.h> /* for seccomp_data */
#include <linux/types.h>
#include <linux/unistd.h>
#include <stddef.h>
#define BPF_LABELS_MAX 256
struct bpf_labels {
int count;
struct __bpf_label {
const char *label;
__u32 location;
} labels[BPF_LABELS_MAX];
};
int bpf_resolve_jumps(struct bpf_labels *labels,
struct sock_filter *filter, size_t count);
__u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label);
void seccomp_bpf_print(struct sock_filter *filter, size_t count);
#define JUMP_JT 0xff
#define JUMP_JF 0xff
#define LABEL_JT 0xfe
#define LABEL_JF 0xfe
#define ALLOW \
BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW)
#define DENY \
BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL)
#define JUMP(labels, label) \
BPF_JUMP(BPF_JMP+BPF_JA, FIND_LABEL((labels), (label)), \
JUMP_JT, JUMP_JF)
#define LABEL(labels, label) \
BPF_JUMP(BPF_JMP+BPF_JA, FIND_LABEL((labels), (label)), \
LABEL_JT, LABEL_JF)
#define SYSCALL(nr, jt) \
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (nr), 0, 1), \
jt
/* Lame, but just an example */
#define FIND_LABEL(labels, label) seccomp_bpf_label((labels), #label)
#define EXPAND(...) __VA_ARGS__
/* Map all width-sensitive operations */
#if __BITS_PER_LONG == 32
#define JEQ(x, jt) JEQ32(x, EXPAND(jt))
#define JNE(x, jt) JNE32(x, EXPAND(jt))
#define JGT(x, jt) JGT32(x, EXPAND(jt))
#define JLT(x, jt) JLT32(x, EXPAND(jt))
#define JGE(x, jt) JGE32(x, EXPAND(jt))
#define JLE(x, jt) JLE32(x, EXPAND(jt))
#define JA(x, jt) JA32(x, EXPAND(jt))
#define ARG(i) ARG_32(i)
#define LO_ARG(idx) offsetof(struct seccomp_data, args[(idx)])
#elif __BITS_PER_LONG == 64
/* Ensure that we load the logically correct offset. */
#if __BYTE_ORDER == __LITTLE_ENDIAN
#define ENDIAN(_lo, _hi) _lo, _hi
#define LO_ARG(idx) offsetof(struct seccomp_data, args[(idx)])
#define HI_ARG(idx) offsetof(struct seccomp_data, args[(idx)]) + sizeof(__u32)
#elif __BYTE_ORDER == __BIG_ENDIAN
#define ENDIAN(_lo, _hi) _hi, _lo
#define LO_ARG(idx) offsetof(struct seccomp_data, args[(idx)]) + sizeof(__u32)
#define HI_ARG(idx) offsetof(struct seccomp_data, args[(idx)])
#else
#error "Unknown endianness"
#endif
union arg64 {
struct {
__u32 ENDIAN(lo32, hi32);
};
__u64 u64;
};
#define JEQ(x, jt) \
JEQ64(((union arg64){.u64 = (x)}).lo32, \
((union arg64){.u64 = (x)}).hi32, \
EXPAND(jt))
#define JGT(x, jt) \
JGT64(((union arg64){.u64 = (x)}).lo32, \
((union arg64){.u64 = (x)}).hi32, \
EXPAND(jt))
#define JGE(x, jt) \
JGE64(((union arg64){.u64 = (x)}).lo32, \
((union arg64){.u64 = (x)}).hi32, \
EXPAND(jt))
#define JNE(x, jt) \
JNE64(((union arg64){.u64 = (x)}).lo32, \
((union arg64){.u64 = (x)}).hi32, \
EXPAND(jt))
#define JLT(x, jt) \
JLT64(((union arg64){.u64 = (x)}).lo32, \
((union arg64){.u64 = (x)}).hi32, \
EXPAND(jt))
#define JLE(x, jt) \
JLE64(((union arg64){.u64 = (x)}).lo32, \
((union arg64){.u64 = (x)}).hi32, \
EXPAND(jt))
#define JA(x, jt) \
JA64(((union arg64){.u64 = (x)}).lo32, \
((union arg64){.u64 = (x)}).hi32, \
EXPAND(jt))
#define ARG(i) ARG_64(i)
#else
#error __BITS_PER_LONG value unusable.
#endif
/* Loads the arg into A */
#define ARG_32(idx) \
BPF_STMT(BPF_LD+BPF_W+BPF_ABS, LO_ARG(idx))
/* Loads hi into A and lo in X */
#define ARG_64(idx) \
BPF_STMT(BPF_LD+BPF_W+BPF_ABS, LO_ARG(idx)), \
BPF_STMT(BPF_ST, 0), /* lo -> M[0] */ \
BPF_STMT(BPF_LD+BPF_W+BPF_ABS, HI_ARG(idx)), \
BPF_STMT(BPF_ST, 1) /* hi -> M[1] */
#define JEQ32(value, jt) \
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (value), 0, 1), \
jt
#define JNE32(value, jt) \
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (value), 1, 0), \
jt
/* Checks the lo, then swaps to check the hi. A=lo,X=hi */
#define JEQ64(lo, hi, jt) \
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (lo), 0, 2), \
BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
jt, \
BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
#define JNE64(lo, hi, jt) \
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 5, 0), \
BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (lo), 2, 0), \
BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
jt, \
BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
#define JA32(value, jt) \
BPF_JUMP(BPF_JMP+BPF_JSET+BPF_K, (value), 0, 1), \
jt
#define JA64(lo, hi, jt) \
BPF_JUMP(BPF_JMP+BPF_JSET+BPF_K, (hi), 3, 0), \
BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
BPF_JUMP(BPF_JMP+BPF_JSET+BPF_K, (lo), 0, 2), \
BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
jt, \
BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
#define JGE32(value, jt) \
BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (value), 0, 1), \
jt
#define JLT32(value, jt) \
BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (value), 1, 0), \
jt
/* Shortcut checking if hi > arg.hi. */
#define JGE64(lo, hi, jt) \
BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (hi), 4, 0), \
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (lo), 0, 2), \
BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
jt, \
BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
#define JLT64(lo, hi, jt) \
BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (hi), 0, 4), \
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (lo), 2, 0), \
BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
jt, \
BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
#define JGT32(value, jt) \
BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (value), 0, 1), \
jt
#define JLE32(value, jt) \
BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (value), 1, 0), \
jt
/* Check hi > args.hi first, then do the GE checking */
#define JGT64(lo, hi, jt) \
BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (hi), 4, 0), \
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (lo), 0, 2), \
BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
jt, \
BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
#define JLE64(lo, hi, jt) \
BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (hi), 6, 0), \
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 3), \
BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (lo), 2, 0), \
BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
jt, \
BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
#define LOAD_SYSCALL_NR \
BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
offsetof(struct seccomp_data, nr))
#endif /* __BPF_HELPER_H__ */
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