This is a note to let you know that I've just added the patch titled

MIPS: BPF: Quit clobbering callee saved registers in JIT code.

to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: mips-bpf-quit-clobbering-callee-saved-registers-in-jit-code.patch and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Sun Mar 18 16:55:33 CET 2018

From: David Daney david.daney@cavium.com Date: Tue, 14 Mar 2017 14:21:43 -0700 Subject: MIPS: BPF: Quit clobbering callee saved registers in JIT code.

From: David Daney david.daney@cavium.com

[ 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 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 Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/mips/net/bpf_jit.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-)

--- 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 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 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_ct 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); }

Patches currently in stable-queue which might be from david.daney@cavium.com are

queue-4.9/mips-bpf-quit-clobbering-callee-saved-registers-in-jit-code.patch queue-4.9/pci-apply-cavium-acs-quirk-only-to-cn81xx-cn83xx-cn88xx-devices.patch queue-4.9/mips-bpf-fix-multiple-problems-in-jit-skb-access-helpers.patch