Just skip the opcode(BPF_ST | BPF_NOSPEC) in the BPF JIT instead of
failing to JIT the entire program, given LoongArch currently has no
couterpart of a speculation barrier instruction. To verify the issue,
use the ltp testcase as shown below.
Also, Wang says:
I can confirm there's currently no speculation barrier equivalent
on LonogArch. (Loongson says there are builtin mitigations for
Spectre-V1 and V2 on their chips, and AFAIK efforts to port the
exploits to mips/LoongArch have all failed a few years ago.)
Without this patch:
$ ./bpf_prog02
[...]
bpf_common.c:123: TBROK: Failed verification: ??? (524)
[...]
Summary:
passed 0
failed 0
broken 1
skipped 0
warnings 0
With this patch:
$ ./bpf_prog02
[...]
Summary:
passed 0
failed 0
broken 0
skipped 0
warnings 0
Fixes: 5dc615520c ("LoongArch: Add BPF JIT support")
Signed-off-by: George Guo <guodongtai@kylinos.cn>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: WANG Xuerui <git@xen0n.name>
Cc: Tiezhu Yang <yangtiezhu@loongson.cn>
Link: https://lore.kernel.org/bpf/20230328071335.2664966-1-guodongtai@kylinos.cn
This patch fixes the following issue of function calls in JIT, like:
[ 29.346981] multi-func JIT bug 105 != 103
The issus can be reproduced by running the "inline simple bpf_loop call"
verifier test.
This is because we are emiting 2-4 instructions for 64-bit immediate moves.
During the first pass of JIT, the placeholder address is zero, emiting two
instructions for it. In the extra pass, the function address is in XKVRANGE,
emiting four instructions for it. This change the instruction index in
JIT context. Let's always use 4 instructions for function address in JIT.
So that the instruction sequences don't change between the first pass and
the extra pass for function calls.
Fixes: 5dc615520c ("LoongArch: Add BPF JIT support")
Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Link: https://lore.kernel.org/bpf/20230214152633.2265699-1-hengqi.chen@gmail.com
Inspired by commit 800834285361("bpf, arm64: Add BPF exception tables"),
do similar to LoongArch to add BPF exception tables.
When a tracing BPF program attempts to read memory without using the
bpf_probe_read() helper, the verifier marks the load instruction with
the BPF_PROBE_MEM flag. Since the LoongArch JIT does not currently
recognize this flag it falls back to the interpreter.
Add support for BPF_PROBE_MEM, by appending an exception table to the
BPF program. If the load instruction causes a data abort, the fixup
infrastructure finds the exception table and fixes up the fault, by
clearing the destination register and jumping over the faulting
instruction.
To keep the compact exception table entry format, inspect the pc in
fixup_exception(). A more generic solution would add a "handler" field
to the table entry, like on x86, s390 and arm64, etc.
Signed-off-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Not all compilers support declare variables in switch-case, so move
declarations to the beginning of a function. Otherwise we may get such
build errors:
arch/loongarch/net/bpf_jit.c: In function ‘emit_atomic’:
arch/loongarch/net/bpf_jit.c:362:3: error: a label can only be part of a statement and a declaration is not a statement
u8 r0 = regmap[BPF_REG_0];
^~
arch/loongarch/net/bpf_jit.c: In function ‘build_insn’:
arch/loongarch/net/bpf_jit.c:727:3: error: a label can only be part of a statement and a declaration is not a statement
u8 t7 = -1;
^~
arch/loongarch/net/bpf_jit.c:778:3: error: a label can only be part of a statement and a declaration is not a statement
int ret;
^~~
arch/loongarch/net/bpf_jit.c:779:3: error: expected expression before ‘u64’
u64 func_addr;
^~~
arch/loongarch/net/bpf_jit.c:780:3: warning: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement]
bool func_addr_fixed;
^~~~
arch/loongarch/net/bpf_jit.c:784:11: error: ‘func_addr’ undeclared (first use in this function); did you mean ‘in_addr’?
&func_addr, &func_addr_fixed);
^~~~~~~~~
in_addr
arch/loongarch/net/bpf_jit.c:784:11: note: each undeclared identifier is reported only once for each function it appears in
arch/loongarch/net/bpf_jit.c:814:3: error: a label can only be part of a statement and a declaration is not a statement
u64 imm64 = (u64)(insn + 1)->imm << 32 | (u32)insn->imm;
^~~
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
BPF programs are normally handled by a BPF interpreter, add BPF JIT
support for LoongArch to allow the kernel to generate native code when
a program is loaded into the kernel. This will significantly speed-up
processing of BPF programs.
Co-developed-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
