| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <CABqD9hbG+KGjURqR_XniDtK4cYJfmOUqACVkeaV1vYEYgkW8xQ@mail.gmail.com>
Date: Mon, 30 Jan 2012 16:52:43 -0600
From: Will Drewry <wad@...omium.org>
To: Corey Bryant <coreyb@...ux.vnet.ibm.com>
Cc: linux-kernel@...r.kernel.org, keescook@...omium.org,
john.johansen@...onical.com, serge.hallyn@...onical.com,
pmoore@...hat.com, eparis@...hat.com, djm@...drot.org,
torvalds@...ux-foundation.org, segoon@...nwall.com,
rostedt@...dmis.org, jmorris@...ei.org, scarybeasts@...il.com,
avi@...hat.com, penberg@...helsinki.fi, viro@...iv.linux.org.uk,
luto@....edu, mingo@...e.hu, akpm@...ux-foundation.org,
khilman@...com, borislav.petkov@....com, amwang@...hat.com,
oleg@...hat.com, ak@...ux.intel.com, eric.dumazet@...il.com,
gregkh@...e.de, dhowells@...hat.com, daniel.lezcano@...e.fr,
linux-fsdevel@...r.kernel.org,
linux-security-module@...r.kernel.org, olofj@...omium.org,
mhalcrow@...gle.com, dlaor@...hat.com, corbet@....net,
alan@...rguk.ukuu.org.uk, indan@....nu, mcgrathr@...omium.org
Subject: Re: [PATCH v6 3/3] Documentation: prctl/seccomp_filter
On Mon, Jan 30, 2012 at 4:47 PM, Corey Bryant <coreyb@...ux.vnet.ibm.com> wrote:
>
>
> On 01/28/2012 05:11 PM, Will Drewry wrote:
>>
>> Documents how system call filtering using Berkeley Packet
>> Filter programs works and how it may be used.
>> Includes an example for x86 (32-bit) and a semi-generic
>> example using an example code generator.
>>
>> v6: - tweak the language to note the requirement of
>> PR_SET_NO_NEW_PRIVS being called prior to use. (luto@....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@...hat.com)
>> - language cleanup (rdunlap@...otime.net)
>> v4: - update for no_new_privs use
>> - minor tweaks
>> v3: - call out BPF<-> Berkeley Packet Filter (rdunlap@...otime.net)
>> - document use of tentative always-unprivileged
>> - guard sample compilation for i386 and x86_64
>> v2: - move code to samples (corbet@....net)
>>
>> Signed-off-by: Will Drewry<wad@...omium.org>
>> ---
>> Documentation/prctl/seccomp_filter.txt | 100 +++++++++++++++
>> samples/Makefile | 2 +-
>> samples/seccomp/Makefile | 27 ++++
>> samples/seccomp/bpf-direct.c | 77 +++++++++++
>> samples/seccomp/bpf-fancy.c | 95 ++++++++++++++
>> samples/seccomp/bpf-helper.c | 89 +++++++++++++
>> samples/seccomp/bpf-helper.h | 219
>> ++++++++++++++++++++++++++++++++
>> 7 files changed, 608 insertions(+), 1 deletions(-)
>> create mode 100644 Documentation/prctl/seccomp_filter.txt
>> create mode 100644 samples/seccomp/Makefile
>> create mode 100644 samples/seccomp/bpf-direct.c
>> create mode 100644 samples/seccomp/bpf-fancy.c
>> create mode 100644 samples/seccomp/bpf-helper.c
>> create mode 100644 samples/seccomp/bpf-helper.h
>>
>> diff --git a/Documentation/prctl/seccomp_filter.txt
>> b/Documentation/prctl/seccomp_filter.txt
>> new file mode 100644
>> index 0000000..4ad7649
>> --- /dev/null
>> +++ b/Documentation/prctl/seccomp_filter.txt
>> @@ -0,0 +1,100 @@
>> + Seccomp filtering
>> + =================
>> +
>> +Introduction
>> +------------
>> +
>> +A large number of system calls are exposed to every userland process
>> +with many of them going unused for the entire lifetime of the process.
>> +As system calls change and mature, bugs are found and eradicated. A
>> +certain subset of userland applications benefit by having a reduced set
>> +of available system calls. The resulting set reduces the total kernel
>> +surface exposed to the application. System call filtering is meant for
>> +use with those applications.
>> +
>> +Seccomp filtering provides a means for a process to specify a filter for
>> +incoming system calls. The filter is expressed as a Berkeley Packet
>> +Filter (BPF) program, as with socket filters, except that the data
>> +operated on is related to the system call being made: system call
>> +number, and the system call arguments. This allows for expressive
>> +filtering of system calls using a filter program language with a long
>> +history of being exposed to userland and a straightforward data set.
>> +
>> +Additionally, BPF makes it impossible for users of seccomp to fall prey
>> +to time-of-check-time-of-use (TOCTOU) attacks that are common in system
>> +call interposition frameworks. BPF programs may not dereference
>> +pointers which constrains all filters to solely evaluating the system
>> +call arguments directly.
>> +
>> +What it isn't
>> +-------------
>> +
>> +System call filtering isn't a sandbox. It provides a clearly defined
>> +mechanism for minimizing the exposed kernel surface. Beyond that,
>> +policy for logical behavior and information flow should be managed with
>> +a combination of other system hardening techniques and, potentially, an
>> +LSM of your choosing. Expressive, dynamic filters provide further
>> options down
>> +this path (avoiding pathological sizes or selecting which of the
>> multiplexed
>> +system calls in socketcall() is allowed, for instance) which could be
>> +construed, incorrectly, as a more complete sandboxing solution.
>> +
>> +Usage
>> +-----
>> +
>> +An additional seccomp mode is added, but they are not directly set by
>> +the consuming process. The new mode, '2', is only available if
>> +CONFIG_SECCOMP_FILTER is set and enabled using prctl with the
>> +PR_ATTACH_SECCOMP_FILTER argument.
>> +
>> +Interacting with seccomp filters is done using one prctl(2) call.
>> +
>> +PR_ATTACH_SECCOMP_FILTER:
>> + Allows the specification of a new filter using a BPF program.
>> + The BPF program will be executed over struct seccomp_filter_data
>> + reflecting the system call number, arguments, and other
>> + metadata, To allow a system call, SECCOMP_BPF_ALLOW must be
>> + returned. At present, all other return values result in the
>> + system call being blocked, but it is recommended to return
>> + SECCOMP_BPF_DENY in those cases. This will allow for future
>> + custom return values to be introduced, if ever desired.
>> +
>> + Usage:
>> + prctl(PR_ATTACH_SECCOMP_FILTER, prog);
>> +
>> + The 'prog' argument is a pointer to a struct sock_fprog which will
>> + contain the filter program. If the program is invalid, the call
>> + will return -1 and set errno to EINVAL.
>> +
>> + Note, is_compat_task is also tracked for the @prog. This means
>> + that once set the calling task will have all of its system calls
>> + blocked if it switches its system call ABI.
>> +
>> + If fork/clone and execve are allowed by @prog, any child processes
>> will
>> + be constrained to the same filters and system call ABI as the
>> parent.
>> +
>> + Prior to use, the task must call prctl(PR_SET_NO_NEW_PRIVS, 1) or
>> + run with CAP_SYS_ADMIN privileges in its namespace. If these are
>> not
>> + true, -EACCES will be returned. This requirement ensures that
>> filter
>> + programs cannot be applied to child processes with greater
>> privileges
>> + than the task that installed them.
>> +
>> + Additionally, if prctl(2) is allowed by the attached filter,
>> + additional filters may be layered on which will increase
>> evaluation
>> + time, but allow for further decreasing the attack surface during
>> + execution of a process.
>> +
>> +The above call returns 0 on success and non-zero on error.
>> +
>> +Example
>> +-------
>> +
>> +The samples/seccomp/ directory contains both a 32-bit specific example
>> +and a more generic example of a higher level macro interface for BPF
>> +program generation.
>> +
>> +Adding architecture support
>> +-----------------------
>> +
>> +Any platform with seccomp support will support seccomp filters as long
>> +as CONFIG_SECCOMP_FILTER is enabled and the architecture has implemented
>> +syscall_get_arguments.
>> diff --git a/samples/Makefile b/samples/Makefile
>> index 6280817..f29b19c 100644
>> --- a/samples/Makefile
>> +++ b/samples/Makefile
>> @@ -1,4 +1,4 @@
>> # Makefile for Linux samples code
>>
>> obj-$(CONFIG_SAMPLES) += kobject/ kprobes/ tracepoints/ trace_events/ \
>> - hw_breakpoint/ kfifo/ kdb/ hidraw/
>> + hw_breakpoint/ kfifo/ kdb/ hidraw/ seccomp/
>> diff --git a/samples/seccomp/Makefile b/samples/seccomp/Makefile
>> new file mode 100644
>> index 0000000..0298c6f
>> --- /dev/null
>> +++ b/samples/seccomp/Makefile
>> @@ -0,0 +1,27 @@
>> +# kbuild trick to avoid linker error. Can be omitted if a module is
>> built.
>> +obj- := dummy.o
>> +
>> +hostprogs-y := bpf-fancy
>> +bpf-fancy-objs := bpf-fancy.o bpf-helper.o
>> +
>> +HOSTCFLAGS_bpf-fancy.o += -I$(objtree)/usr/include
>> +HOSTCFLAGS_bpf-fancy.o += -idirafter $(objtree)/include
>> +HOSTCFLAGS_bpf-helper.o += -I$(objtree)/usr/include
>> +HOSTCFLAGS_bpf-helper.o += -idirafter $(objtree)/include
>> +
>> +# bpf-direct.c is x86-only.
>> +ifeq ($(filter-out x86_64 i386,$(KBUILD_BUILDHOST)),)
>> +# List of programs to build
>> +hostprogs-y += bpf-direct
>> +bpf-direct-objs := bpf-direct.o
>> +endif
>> +
>> +# Tell kbuild to always build the programs
>> +always := $(hostprogs-y)
>> +
>> +HOSTCFLAGS_bpf-direct.o += -I$(objtree)/usr/include
>> +HOSTCFLAGS_bpf-direct.o += -idirafter $(objtree)/include
>> +ifeq ($(KBUILD_BUILDHOST),x86_64)
>> +HOSTCFLAGS_bpf-direct.o += -m32
>> +HOSTLOADLIBES_bpf-direct += -m32
>> +endif
>> diff --git a/samples/seccomp/bpf-direct.c b/samples/seccomp/bpf-direct.c
>> new file mode 100644
>> index 0000000..d799244
>> --- /dev/null
>> +++ b/samples/seccomp/bpf-direct.c
>> @@ -0,0 +1,77 @@
>> +/*
>> + * 32-bit seccomp filter example with BPF macros
>> + *
>> + * Copyright (c) 2012 The Chromium OS
>> Authors<chromium-os-dev@...omium.org>
>> + * Author: Will Drewry<wad@...omium.org>
>> + *
>> + * The code may be used by anyone for any purpose,
>> + * and can serve as a starting point for developing
>> + * applications using prctl(PR_ATTACH_SECCOMP_FILTER).
>> + */
>> +
>> +#include<linux/filter.h>
>> +#include<linux/ptrace.h>
>> +#include<linux/seccomp_filter.h>
>> +#include<linux/unistd.h>
>> +#include<stdio.h>
>> +#include<stddef.h>
>> +#include<sys/prctl.h>
>> +#include<unistd.h>
>> +
>> +#ifndef PR_ATTACH_SECCOMP_FILTER
>> +# define PR_ATTACH_SECCOMP_FILTER 37
>> +#endif
>> +
>> +#define syscall_arg(_n) (offsetof(struct seccomp_filter_data,
>> args[_n].lo32))
>> +#define nr (offsetof(struct seccomp_filter_data, syscall_nr))
>> +
>> +static int install_filter(void)
>> +{
>> + struct seccomp_filter_block filter[] = {
>> + /* Grab the system call number */
>> + BPF_STMT(BPF_LD+BPF_W+BPF_ABS, nr),
>> + /* Jump table for the allowed syscalls */
>> + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_rt_sigreturn, 10, 0),
>> + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_sigreturn, 9, 0),
>> + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_exit_group, 8, 0),
>> + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_exit, 7, 0),
>> + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_read, 1, 0),
>> + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_write, 2, 6),
>> +
>> + /* Check that read is only using stdin. */
>> + BPF_STMT(BPF_LD+BPF_W+BPF_ABS, syscall_arg(0)),
>> + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, STDIN_FILENO, 3, 4),
>> +
>> + /* Check that write is only using stdout/stderr */
>> + BPF_STMT(BPF_LD+BPF_W+BPF_ABS, syscall_arg(0)),
>> + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, STDOUT_FILENO, 1, 0),
>> + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, STDERR_FILENO, 0, 1),
>> +
>> + BPF_STMT(BPF_RET+BPF_K, SECCOMP_BPF_ALLOW),
>> + BPF_STMT(BPF_RET+BPF_K, SECCOMP_BPF_DENY),
>> + };
>> + struct seccomp_fprog prog = {
>> + .len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
>> + .filter = filter,
>> + };
>> + if (prctl(PR_ATTACH_SECCOMP_FILTER,&prog)) {
>> + perror("prctl");
>> + return 1;
>> + }
>> + return 0;
>> +}
>> +
>> +#define payload(_c) (_c), sizeof((_c))
>> +int main(int argc, char **argv)
>> +{
>> + char buf[4096];
>> + ssize_t bytes = 0;
>> + if (install_filter())
>> + return 1;
>> + syscall(__NR_write, STDOUT_FILENO,
>> + payload("OHAI! WHAT IS YOUR NAME? "));
>> + bytes = syscall(__NR_read, STDIN_FILENO, buf, sizeof(buf));
>> + syscall(__NR_write, STDOUT_FILENO, payload("HELLO, "));
>> + syscall(__NR_write, STDOUT_FILENO, buf, bytes);
>> + return 0;
>> +}
>> diff --git a/samples/seccomp/bpf-fancy.c b/samples/seccomp/bpf-fancy.c
>> new file mode 100644
>> index 0000000..1318b1a
>> --- /dev/null
>> +++ b/samples/seccomp/bpf-fancy.c
>> @@ -0,0 +1,95 @@
>> +/*
>> + * Seccomp BPF example using a macro-based generator.
>> + *
>> + * Copyright (c) 2012 The Chromium OS
>> Authors<chromium-os-dev@...omium.org>
>> + * Author: Will Drewry<wad@...omium.org>
>> + *
>> + * The code may be used by anyone for any purpose,
>> + * and can serve as a starting point for developing
>> + * applications using prctl(PR_ATTACH_SECCOMP_FILTER).
>> + */
>> +
>> +#include<linux/seccomp_filter.h>
>> +#include<linux/unistd.h>
>> +#include<stdio.h>
>> +#include<string.h>
>> +#include<sys/prctl.h>
>> +#include<unistd.h>
>> +
>> +#include "bpf-helper.h"
>> +
>> +#ifndef PR_ATTACH_SECCOMP_FILTER
>> +# define PR_ATTACH_SECCOMP_FILTER 37
>> +#endif
>> +
>> +int main(int argc, char **argv)
>> +{
>> + struct bpf_labels l;
>> + static const char msg1[] = "Please type something: ";
>> + static const char msg2[] = "You typed: ";
>> + char buf[256];
>> + struct seccomp_filter_block filter[] = {
>> + LOAD_SYSCALL_NR,
>> + SYSCALL(__NR_exit, ALLOW),
>> + SYSCALL(__NR_exit_group, ALLOW),
>> + SYSCALL(__NR_write, JUMP(&l, write_fd)),
>> + SYSCALL(__NR_read, JUMP(&l, read)),
>> + DENY, /* Don't passthrough into a label */
>> +
>> + LABEL(&l, read),
>> + ARG(0),
>> + JNE(STDIN_FILENO, DENY),
>> + ARG(1),
>> + JNE((unsigned long)buf, DENY),
>> + ARG(2),
>> + JGE(sizeof(buf), DENY),
>> + ALLOW,
>> +
>> + LABEL(&l, write_fd),
>> + ARG(0),
>> + JEQ(STDOUT_FILENO, JUMP(&l, write_buf)),
>> + JEQ(STDERR_FILENO, JUMP(&l, write_buf)),
>> + DENY,
>> +
>> + LABEL(&l, write_buf),
>> + ARG(1),
>> + JEQ((unsigned long)msg1, JUMP(&l, msg1_len)),
>> + JEQ((unsigned long)msg2, JUMP(&l, msg2_len)),
>> + JEQ((unsigned long)buf, JUMP(&l, buf_len)),
>> + DENY,
>> +
>> + LABEL(&l, msg1_len),
>> + ARG(2),
>> + JLT(sizeof(msg1), ALLOW),
>> + DENY,
>> +
>> + LABEL(&l, msg2_len),
>> + ARG(2),
>> + JLT(sizeof(msg2), ALLOW),
>> + DENY,
>> +
>> + LABEL(&l, buf_len),
>> + ARG(2),
>> + JLT(sizeof(buf), ALLOW),
>> + DENY,
>> + };
>> + struct seccomp_fprog prog = {
>> + .len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
>> + .filter = filter,
>> + };
>> + ssize_t bytes;
>> + bpf_resolve_jumps(&l, filter, sizeof(filter)/sizeof(*filter));
>> +
>> + if (prctl(PR_ATTACH_SECCOMP_FILTER,&prog)) {
>> + perror("prctl");
>> + return 1;
>> + }
>> + syscall(__NR_write, STDOUT_FILENO, msg1, strlen(msg1));
>> + bytes = syscall(__NR_read, STDIN_FILENO, buf, sizeof(buf)-1);
>> + bytes = (bytes> 0 ? bytes : 0);
>> + syscall(__NR_write, STDERR_FILENO, msg2, strlen(msg2));
>> + syscall(__NR_write, STDERR_FILENO, buf, bytes);
>> + /* Now get killed */
>> + syscall(__NR_write, STDERR_FILENO, msg2, strlen(msg2)+2);
>> + return 0;
>> +}
>> diff --git a/samples/seccomp/bpf-helper.c b/samples/seccomp/bpf-helper.c
>> new file mode 100644
>> index 0000000..e1b6bc7
>> --- /dev/null
>> +++ b/samples/seccomp/bpf-helper.c
>> @@ -0,0 +1,89 @@
>> +/*
>> + * Seccomp BPF helper functions
>> + *
>> + * Copyright (c) 2012 The Chromium OS
>> Authors<chromium-os-dev@...omium.org>
>> + * Author: Will Drewry<wad@...omium.org>
>> + *
>> + * The code may be used by anyone for any purpose,
>> + * and can serve as a starting point for developing
>> + * applications using prctl(PR_ATTACH_SECCOMP_FILTER).
>> + */
>> +
>> +#include<stdio.h>
>> +#include<string.h>
>> +
>> +#include "bpf-helper.h"
>> +
>> +int bpf_resolve_jumps(struct bpf_labels *labels,
>> + struct seccomp_filter_block *filter, size_t count)
>> +{
>> + struct seccomp_filter_block *begin = filter;
>> + __u8 insn = count - 1;
>> +
>> + if (count< 1)
>> + return -1;
>> + /*
>> + * Walk it once, backwards, to build the label table and do fixups.
>> + * Since backward jumps are disallowed by BPF, this is easy.
>> + */
>> + filter += insn;
>> + for (; filter>= begin; --insn, --filter) {
>> + if (filter->code != (BPF_JMP+BPF_JA))
>> + continue;
>> + switch ((filter->jt<<8)|filter->jf) {
>> + case (JUMP_JT<<8)|JUMP_JF:
>> + if (labels->labels[filter->k].location ==
>> 0xffffffff) {
>> + fprintf(stderr, "Unresolved label:
>> '%s'\n",
>> + labels->labels[filter->k].label);
>> + return 1;
>> + }
>> + filter->k = labels->labels[filter->k].location -
>> + (insn + 1);
>> + filter->jt = 0;
>> + filter->jf = 0;
>> + continue;
>> + case (LABEL_JT<<8)|LABEL_JF:
>> + if (labels->labels[filter->k].location !=
>> 0xffffffff) {
>> + fprintf(stderr, "Duplicate label use:
>> '%s'\n",
>> + labels->labels[filter->k].label);
>> + return 1;
>> + }
>> + labels->labels[filter->k].location = insn;
>> + filter->k = 0; /* fall through */
>> + filter->jt = 0;
>> + filter->jf = 0;
>> + continue;
>> + }
>> + }
>> + return 0;
>> +}
>> +
>> +/* Simple lookup table for labels. */
>> +__u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label)
>> +{
>> + struct __bpf_label *begin = labels->labels, *end;
>> + int id;
>> + if (labels->count == 0) {
>> + begin->label = label;
>> + begin->location = 0xffffffff;
>> + labels->count++;
>> + return 0;
>> + }
>> + end = begin + labels->count;
>> + for (id = 0; begin< end; ++begin, ++id) {
>> + if (!strcmp(label, begin->label))
>> + return id;
>> + }
>> + begin->label = label;
>> + begin->location = 0xffffffff;
>> + labels->count++;
>> + return id;
>> +}
>> +
>> +void seccomp_bpf_print(struct seccomp_filter_block *filter, size_t count)
>> +{
>> + struct seccomp_filter_block *end = filter + count;
>> + for ( ; filter< end; ++filter)
>> + printf("{ code=%u,jt=%u,jf=%u,k=%u },\n",
>> + filter->code, filter->jt, filter->jf, filter->k);
>> +}
>> diff --git a/samples/seccomp/bpf-helper.h b/samples/seccomp/bpf-helper.h
>> new file mode 100644
>> index 0000000..92b94ec
>> --- /dev/null
>> +++ b/samples/seccomp/bpf-helper.h
>> @@ -0,0 +1,219 @@
>> +/*
>> + * Example wrapper around BPF macros.
>> + *
>> + * Copyright (c) 2012 The Chromium OS
>> Authors<chromium-os-dev@...omium.org>
>> + * Author: Will Drewry<wad@...omium.org>
>> + *
>> + * The code may be used by anyone for any purpose,
>> + * and can serve as a starting point for developing
>> + * applications using prctl(PR_ATTACH_SECCOMP_FILTER).
>> + *
>> + * 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<linux/filter.h>
>> +#include<linux/seccomp_filter.h> /* for seccomp_filter_data.arg */
>> +#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 seccomp_filter_block *filter, size_t count);
>> +__u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label);
>> +void seccomp_bpf_print(struct seccomp_filter_block *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, 0xFFFFFFFF)
>> +#define DENY \
>> + BPF_STMT(BPF_RET+BPF_K, 0)
>> +#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)
>> +
>> +#elif __BITS_PER_LONG == 64
>> +
>> +#define JEQ(x, jt) \
>> + JEQ64(((union seccomp_filter_arg){.u64 = (x)}).lo32, \
>> + ((union seccomp_filter_arg){.u64 = (x)}).hi32, \
>> + EXPAND(jt))
>> +#define JGT(x, jt) \
>> + JGT64(((union seccomp_filter_arg){.u64 = (x)}).lo32, \
>> + ((union seccomp_filter_arg){.u64 = (x)}).hi32, \
>> + EXPAND(jt))
>> +#define JGE(x, jt) \
>> + JGE64(((union seccomp_filter_arg){.u64 = (x)}).lo32, \
>> + ((union seccomp_filter_arg){.u64 = (x)}).hi32, \
>> + EXPAND(jt))
>> +#define JNE(x, jt) \
>> + JNE64(((union seccomp_filter_arg){.u64 = (x)}).lo32, \
>> + ((union seccomp_filter_arg){.u64 = (x)}).hi32, \
>> + EXPAND(jt))
>> +#define JLT(x, jt) \
>> + JLT64(((union seccomp_filter_arg){.u64 = (x)}).lo32, \
>> + ((union seccomp_filter_arg){.u64 = (x)}).hi32, \
>> + EXPAND(jt))
>> +#define JLE(x, jt) \
>> + JLE64(((union seccomp_filter_arg){.u64 = (x)}).lo32, \
>> + ((union seccomp_filter_arg){.u64 = (x)}).hi32, \
>> + EXPAND(jt))
>> +
>> +#define JA(x, jt) \
>> + JA64(((union seccomp_filter_arg){.u64 = (x)}).lo32, \
>> + ((union seccomp_filter_arg){.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, \
>> + offsetof(struct seccomp_filter_data, args[(idx)].lo32))
>> +
>> +/* Loads hi into A and lo in X */
>> +#define ARG_64(idx) \
>> + BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
>> + offsetof(struct seccomp_filter_data, args[(idx)].lo32)), \
>> + BPF_STMT(BPF_ST, 0), /* lo -> M[0] */ \
>> + BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
>> + offsetof(struct seccomp_filter_data, args[(idx)].hi32)), \
>> + 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), 0, 1), \
>> + jt
>
>
> Should the true/false offsets be reversed here?
Looks that way :)
> Thanks for all the work on this. We're looking forward to using it with
> QEMU.
Definitely - thanks!
will
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists