linux-kernel - [PATCH mips-fixes] MIPS: BPF: eBPF JIT: check for MIPS ISA compliance in Kconfig

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Message-Id: <20191206080741.12306-1-alobakin@dlink.ru>
Date:   Fri,  6 Dec 2019 11:07:41 +0300
From:   Alexander Lobakin <alobakin@...nk.ru>
To:     Paul Burton <paulburton@...nel.org>
Cc:     Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>,
        Hassan Naveed <hnaveed@...ecomp.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        Alexander Lobakin <alobakin@...nk.ru>,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org, stable@...r.kernel.org
Subject: [PATCH mips-fixes] MIPS: BPF: eBPF JIT: check for MIPS ISA compliance in Kconfig

It is completely wrong to check for compile-time MIPS ISA revision in
the body of bpf_int_jit_compile() as it may lead to get MIPS JIT fully
omitted by the CC while the rest system will think that the JIT is
actually present and works [1].
We can check if the selected CPU really supports MIPS eBPF JIT at
configure time and avoid such situations when kernel can be built
without both JIT and interpreter, but with CONFIG_BPF_SYSCALL=y.

[1] https://lore.kernel.org/linux-mips/09d713a59665d745e21d021deeaebe0a@dlink.ru/

Fixes: 716850ab104d ("MIPS: eBPF: Initial eBPF support for MIPS32 architecture.")
Cc: <stable@...r.kernel.org> # v5.2+
Signed-off-by: Alexander Lobakin <alobakin@...nk.ru>
---
 arch/mips/Kconfig        | 2 +-
 arch/mips/net/ebpf_jit.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index add388236f4e..407b85ee93e4 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -47,7 +47,7 @@ config MIPS
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE if CPU_SUPPORTS_HUGEPAGES
 	select HAVE_ASM_MODVERSIONS
-	select HAVE_EBPF_JIT if (!CPU_MICROMIPS)
+	select HAVE_EBPF_JIT if !CPU_MICROMIPS && TARGET_ISA_REV >= 2
 	select HAVE_CONTEXT_TRACKING
 	select HAVE_COPY_THREAD_TLS
 	select HAVE_C_RECORDMCOUNT
diff --git a/arch/mips/net/ebpf_jit.c b/arch/mips/net/ebpf_jit.c
index 46b76751f3a5..a2405d5f7d1e 100644
--- a/arch/mips/net/ebpf_jit.c
+++ b/arch/mips/net/ebpf_jit.c
@@ -1803,7 +1803,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
 	unsigned int image_size;
 	u8 *image_ptr;
 
-	if (!prog->jit_requested || MIPS_ISA_REV < 2)
+	if (!prog->jit_requested)
 		return prog;
 
 	tmp = bpf_jit_blind_constants(prog);
-- 
2.24.0