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Hill" , "linux-mips@linux-mips.org" , "netdev@vger.kernel.org" , Ralf Baechle , Sasha Levin Subject: [PATCH AUTOSEL for 4.4 067/115] MIPS: BPF: Quit clobbering callee saved registers in JIT code. Thread-Topic: [PATCH AUTOSEL for 4.4 067/115] MIPS: BPF: Quit clobbering callee saved registers in JIT code. 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If it is not used, we don't save and restore it, so the clearing has the nasty side effect of clobbering caller state. Also, don't emit stack pointer adjustment instructions if the adjustment amount is zero. Signed-off-by: David Daney Cc: James Hogan Cc: Alexei Starovoitov Cc: Steven J. Hill Cc: linux-mips@linux-mips.org Cc: netdev@vger.kernel.org Cc: linux-kernel@vger.kernel.org Patchwork: https://patchwork.linux-mips.org/patch/15745/ Signed-off-by: Ralf Baechle Signed-off-by: Sasha Levin --- arch/mips/net/bpf_jit.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/arch/mips/net/bpf_jit.c b/arch/mips/net/bpf_jit.c index 1a8c96035716..c0c1e9529dbd 100644 --- a/arch/mips/net/bpf_jit.c +++ b/arch/mips/net/bpf_jit.c @@ -527,7 +527,8 @@ static void save_bpf_jit_regs(struct jit_ctx *ctx, unsi= gned offset) u32 sflags, tmp_flags; =20 /* Adjust the stack pointer */ - emit_stack_offset(-align_sp(offset), ctx); + if (offset) + emit_stack_offset(-align_sp(offset), ctx); =20 tmp_flags =3D sflags =3D ctx->flags >> SEEN_SREG_SFT; /* sflags is essentially a bitmap */ @@ -579,7 +580,8 @@ static void restore_bpf_jit_regs(struct jit_ctx *ctx, emit_load_stack_reg(r_ra, r_sp, real_off, ctx); =20 /* Restore the sp and discard the scrach memory */ - emit_stack_offset(align_sp(offset), ctx); + if (offset) + emit_stack_offset(align_sp(offset), ctx); } =20 static unsigned int get_stack_depth(struct jit_ctx *ctx) @@ -626,8 +628,14 @@ static void build_prologue(struct jit_ctx *ctx) if (ctx->flags & SEEN_X) emit_jit_reg_move(r_X, r_zero, ctx); =20 - /* Do not leak kernel data to userspace */ - if (bpf_needs_clear_a(&ctx->skf->insns[0])) + /* + * Do not leak kernel data to userspace, we only need to clear + * r_A if it is ever used. In fact if it is never used, we + * will not save/restore it, so clearing it in this case would + * corrupt the state of the caller. + */ + if (bpf_needs_clear_a(&ctx->skf->insns[0]) && + (ctx->flags & SEEN_A)) emit_jit_reg_move(r_A, r_zero, ctx); } =20 --=20 2.14.1