[PATCH AUTOSEL for 4.9 136/219] MIPS: BPF: Quit clobbering callee saved registers in JIT code.
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From: Sasha Levin <hidden>
Date: 2018-03-03 22:35:09
Also in:
lkml, netdev, stable
Subsystem:
bpf jit for mips (32-bit and 64-bit), bpf [general] (safe dynamic programs and tools), mips, the rest · Maintainers:
Johan Almbladh, Paul Burton, Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Thomas Bogendoerfer, Linus Torvalds
From: David Daney <redacted> [ Upstream commit 1ef0910cfd681f0bd0b81f8809935b2006e9cfb9 ] 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 <redacted> Cc: James Hogan <redacted> Cc: Alexei Starovoitov <ast@kernel.org> Cc: Steven J. Hill <redacted> 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 <redacted> Signed-off-by: Sasha Levin <redacted> --- 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 49a2e2226fee..248603739198 100644
--- a/arch/mips/net/bpf_jit.c
+++ b/arch/mips/net/bpf_jit.c@@ -526,7 +526,8 @@ static void save_bpf_jit_regs(struct jit_ctx *ctx, unsigned offset) u32 sflags, tmp_flags; /* Adjust the stack pointer */ - emit_stack_offset(-align_sp(offset), ctx); + if (offset) + emit_stack_offset(-align_sp(offset), ctx); tmp_flags = sflags = ctx->flags >> SEEN_SREG_SFT; /* sflags is essentially a bitmap */
@@ -578,7 +579,8 @@ 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 */ - emit_stack_offset(align_sp(offset), ctx); + if (offset) + emit_stack_offset(align_sp(offset), ctx); } static unsigned int get_stack_depth(struct jit_ctx *ctx)
@@ -625,8 +627,14 @@ 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); }
--
2.14.1