linux-kernel - [PATCH 5.14 080/849] bpf: Prevent increasing bpf_jit

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Message-Id: <20211115165422.765418824@linuxfoundation.org>
Date:   Mon, 15 Nov 2021 17:52:43 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Lorenz Bauer <lmb@...udflare.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.14 080/849] bpf: Prevent increasing bpf_jit_limit above max

From: Lorenz Bauer <lmb@...udflare.com>

[ Upstream commit fadb7ff1a6c2c565af56b4aacdd086b067eed440 ]

Restrict bpf_jit_limit to the maximum supported by the arch's JIT.

Signed-off-by: Lorenz Bauer <lmb@...udflare.com>
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Link: https://lore.kernel.org/bpf/20211014142554.53120-4-lmb@cloudflare.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 include/linux/filter.h     | 1 +
 kernel/bpf/core.c          | 4 +++-
 net/core/sysctl_net_core.c | 2 +-
 3 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 83b896044e79f..c227c45121d6a 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1027,6 +1027,7 @@ extern int bpf_jit_enable;
 extern int bpf_jit_harden;
 extern int bpf_jit_kallsyms;
 extern long bpf_jit_limit;
+extern long bpf_jit_limit_max;
 
 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 4c0c0146f956c..2340d11737cca 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -524,6 +524,7 @@ int bpf_jit_enable   __read_mostly = IS_BUILTIN(CONFIG_BPF_JIT_DEFAULT_ON);
 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;
 
 static void
 bpf_prog_ksym_set_addr(struct bpf_prog *prog)
@@ -817,7 +818,8 @@ u64 __weak bpf_jit_alloc_exec_limit(void)
 static int __init bpf_jit_charge_init(void)
 {
 	/* Only used as heuristic here to derive limit. */
-	bpf_jit_limit = min_t(u64, round_up(bpf_jit_alloc_exec_limit() >> 2,
+	bpf_jit_limit_max = bpf_jit_alloc_exec_limit();
+	bpf_jit_limit = min_t(u64, round_up(bpf_jit_limit_max >> 2,
 					    PAGE_SIZE), LONG_MAX);
 	return 0;
 }
diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index c8496c1142c9d..5f88526ad61cc 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -419,7 +419,7 @@ static struct ctl_table net_core_table[] = {
 		.mode		= 0600,
 		.proc_handler	= proc_dolongvec_minmax_bpf_restricted,
 		.extra1		= &long_one,
-		.extra2		= &long_max,
+		.extra2		= &bpf_jit_limit_max,
 	},
 #endif
 	{
-- 
2.33.0