MIPS: BPF: Quit clobbering callee saved registers in JIT code. (1ef0910c) · Commits · 戴 / test

If bpf_needs_clear_a() returns true, only actually clear it if it is ever used. 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 <david.daney@cavium.com> Cc: James Hogan <james.hogan@imgtec.com> Cc: Alexei Starovoitov <ast@kernel.org> Cc: Steven J. Hill <steven.hill@cavium.com> 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 <ralf@linux-mips.org>

arch/mips/net/bpf_jit.c

+12 −4

Original line number	Diff line number	Diff line
		@@ -532,6 +532,7 @@ static void save_bpf_jit_regs(struct jit_ctx *ctx, unsigned offset)
		u32 sflags, tmp_flags;

		/* Adjust the stack pointer */
		if (offset)
		emit_stack_offset(-align_sp(offset), ctx);

		tmp_flags = sflags = ctx->flags >> SEEN_SREG_SFT;
		@@ -584,6 +585,7 @@ static void restore_bpf_jit_regs(struct jit_ctx *ctx,
		emit_load_stack_reg(r_ra, r_sp, real_off, ctx);

		/* Restore the sp and discard the scrach memory */
		if (offset)
		emit_stack_offset(align_sp(offset), ctx);
		}

		@@ -631,8 +633,14 @@ static void build_prologue(struct jit_ctx *ctx)
		if (ctx->flags & SEEN_X)
		emit_jit_reg_move(r_X, r_zero, ctx);

		/* 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);
		}

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