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SubjectRe: [PATCH v6 3/3] Documentation: prctl/seccomp_filter


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@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: Will Drewry<wad@chromium.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@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_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@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_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@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_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@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_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?

Thanks for all the work on this. We're looking forward to using it with
QEMU.

> +
> +/* 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_filter_data, syscall_nr))
> +
> +#endif /* __BPF_HELPER_H__ */


--
Regards,
Corey



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