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| author | Daniel Borkmann <daniel@iogearbox.net> | 2021-08-27 10:55:31 -0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-09-03 09:58:00 +0200 |
| commit | c348d806ed1d3075af52345344243824d72c4945 (patch) | |
| tree | 9046375af505fdb243412550f9ca86d1ea11006c | |
| parent | ce7d8be2eaa4cab3032e256d154d1c33843d2367 (diff) | |
| download | linux-stable-c348d806ed1d3075af52345344243824d72c4945.tar.gz linux-stable-c348d806ed1d3075af52345344243824d72c4945.tar.bz2 linux-stable-c348d806ed1d3075af52345344243824d72c4945.zip | |
bpf: Do not use ax register in interpreter on div/mod
Partially undo old commit 144cd91c4c2b ("bpf: move tmp variable into ax
register in interpreter"). The reason we need this here is because ax
register will be used for holding temporary state for div/mod instruction
which otherwise interpreter would corrupt. This will cause a small +8 byte
stack increase for interpreter, but with the gain that we can use it from
verifier rewrites as scratch register.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
[cascardo: This partial revert is needed in order to support using AX for
the following two commits, as there is no JMP32 on 4.19.y]
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | kernel/bpf/core.c | 32 |
1 files changed, 15 insertions, 17 deletions
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 36be400c3e65..d2b6d2459aad 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -705,9 +705,6 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from, * below. * * Constant blinding is only used by JITs, not in the interpreter. - * The interpreter uses AX in some occasions as a local temporary - * register e.g. in DIV or MOD instructions. - * * In restricted circumstances, the verifier can also use the AX * register for rewrites as long as they do not interfere with * the above cases! @@ -1057,6 +1054,7 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack) #undef BPF_INSN_3_LBL #undef BPF_INSN_2_LBL u32 tail_call_cnt = 0; + u64 tmp; #define CONT ({ insn++; goto select_insn; }) #define CONT_JMP ({ insn++; goto select_insn; }) @@ -1117,36 +1115,36 @@ select_insn: (*(s64 *) &DST) >>= IMM; CONT; ALU64_MOD_X: - div64_u64_rem(DST, SRC, &AX); - DST = AX; + div64_u64_rem(DST, SRC, &tmp); + DST = tmp; CONT; ALU_MOD_X: - AX = (u32) DST; - DST = do_div(AX, (u32) SRC); + tmp = (u32) DST; + DST = do_div(tmp, (u32) SRC); CONT; ALU64_MOD_K: - div64_u64_rem(DST, IMM, &AX); - DST = AX; + div64_u64_rem(DST, IMM, &tmp); + DST = tmp; CONT; ALU_MOD_K: - AX = (u32) DST; - DST = do_div(AX, (u32) IMM); + tmp = (u32) DST; + DST = do_div(tmp, (u32) IMM); CONT; ALU64_DIV_X: DST = div64_u64(DST, SRC); CONT; ALU_DIV_X: - AX = (u32) DST; - do_div(AX, (u32) SRC); - DST = (u32) AX; + tmp = (u32) DST; + do_div(tmp, (u32) SRC); + DST = (u32) tmp; CONT; ALU64_DIV_K: DST = div64_u64(DST, IMM); CONT; ALU_DIV_K: - AX = (u32) DST; - do_div(AX, (u32) IMM); - DST = (u32) AX; + tmp = (u32) DST; + do_div(tmp, (u32) IMM); + DST = (u32) tmp; CONT; ALU_END_TO_BE: switch (IMM) { |