linux-kernel - [PATCH v2 4/4] bpf: export bpf_jit

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Date:   Tue, 12 Oct 2021 14:59:35 +0100
From:   Lorenz Bauer <lmb@...udflare.com>
To:     nicolas.dichtel@...nd.com, luke.r.nels@...il.com,
        Jonathan Corbet <corbet@....net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     kernel-team@...udflare.com, Lorenz Bauer <lmb@...udflare.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: [PATCH v2 4/4] bpf: export bpf_jit_current

Expose bpf_jit_current as a read only value via sysctl.

Signed-off-by: Lorenz Bauer <lmb@...udflare.com>
---
 Documentation/admin-guide/sysctl/net.rst |  6 ++++++
 include/linux/filter.h                   |  1 +
 kernel/bpf/core.c                        |  3 +--
 net/core/sysctl_net_core.c               | 24 ++++++++++++++++++++++++
 4 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst
index 4150f74c521a..524e7db8d53f 100644
--- a/Documentation/admin-guide/sysctl/net.rst
+++ b/Documentation/admin-guide/sysctl/net.rst
@@ -123,6 +123,12 @@ compiler in order to reject unprivileged JIT requests once it has
 been surpassed. bpf_jit_limit contains the value of the global limit
 in bytes.
 
+bpf_jit_current
+---------------
+
+The amount of JIT memory currently allocated, in bytes. JITing of
+unprivileged BPF is rejected if this value is above bpf_jit_limit.
+
 dev_weight
 ----------
 
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 8231a6a257f6..42c543a21cd8 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1051,6 +1051,7 @@ extern int bpf_jit_harden;
 extern int bpf_jit_kallsyms;
 extern long bpf_jit_limit;
 extern long bpf_jit_limit_max;
+extern atomic_long_t bpf_jit_current;
 
 typedef void (*bpf_jit_fill_hole_t)(void *area, unsigned int size);
 
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index ab84b3816339..12aedab09222 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -526,6 +526,7 @@ int bpf_jit_kallsyms __read_mostly = IS_BUILTIN(CONFIG_BPF_JIT_DEFAULT_ON);
 int bpf_jit_harden   __read_mostly;
 long bpf_jit_limit   __read_mostly;
 long bpf_jit_limit_max __read_mostly;
+atomic_long_t bpf_jit_current __read_mostly;
 
 static void
 bpf_prog_ksym_set_addr(struct bpf_prog *prog)
@@ -801,8 +802,6 @@ int bpf_jit_add_poke_descriptor(struct bpf_prog *prog,
 	return slot;
 }
 
-static atomic_long_t bpf_jit_current;
-
 /* Can be overridden by an arch's JIT compiler if it has a custom,
  * dedicated BPF backend memory area, or if neither of the two
  * below apply.
diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index 5f88526ad61c..78603f561482 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -15,6 +15,7 @@
 #include <linux/vmalloc.h>
 #include <linux/init.h>
 #include <linux/slab.h>
+#include <linux/atomic.h>
 
 #include <net/ip.h>
 #include <net/sock.h>
@@ -307,6 +308,22 @@ proc_dolongvec_minmax_bpf_restricted(struct ctl_table *table, int write,
 
 	return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 }
+
+static int proc_bpf_jit_current(struct ctl_table *table, int write,
+				void *buffer, size_t *lenp, loff_t *ppos)
+{
+	long curr = atomic_long_read(&bpf_jit_current) << PAGE_SHIFT;
+	struct ctl_table ctl_entry = {
+		.data		= &curr,
+		.maxlen		= sizeof(long),
+	};
+
+
+	if (!capable(CAP_SYS_ADMIN) || write)
+		return -EPERM;
+
+	return proc_doulongvec_minmax(&ctl_entry, write, buffer, lenp, ppos);
+}
 #endif
 
 static struct ctl_table net_core_table[] = {
@@ -421,6 +438,13 @@ static struct ctl_table net_core_table[] = {
 		.extra1		= &long_one,
 		.extra2		= &bpf_jit_limit_max,
 	},
+	{
+		.procname	= "bpf_jit_current",
+		.data		= &bpf_jit_current,
+		.maxlen		= sizeof(long),
+		.mode		= 0400,
+		.proc_handler	= proc_bpf_jit_current,
+	},
 #endif
 	{
 		.procname	= "netdev_tstamp_prequeue",
-- 
2.30.2