Re: [PATCH] powerpc/bpf: Use bctrl for making function calls

[Christophe Leroy <christophe.leroy@xxxxxxxxxx>]

Le 09/06/2021 à 11:00, Naveen N. Rao a écrit :
> blrl corrupts the link stack. Instead use bctrl when making function
> calls from BPF programs.

What's the link stack ? Is it the PPC64 branch predictor stack ?

> Reported-by: Anton Blanchard <anton@xxxxxxxxxx>
> Signed-off-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
> ---
>   arch/powerpc/include/asm/ppc-opcode.h |  1 +
>   arch/powerpc/net/bpf_jit_comp32.c     |  4 ++--
>   arch/powerpc/net/bpf_jit_comp64.c     | 12 ++++++------
>   3 files changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/ppc-opcode.h b/arch/powerpc/include/asm/ppc-opcode.h
> index ac41776661e963..1abacb8417d562 100644
> --- a/arch/powerpc/include/asm/ppc-opcode.h
> +++ b/arch/powerpc/include/asm/ppc-opcode.h
> @@ -451,6 +451,7 @@
>   #define PPC_RAW_MTLR(r)			(0x7c0803a6 | ___PPC_RT(r))
>   #define PPC_RAW_MFLR(t)			(PPC_INST_MFLR | ___PPC_RT(t))
>   #define PPC_RAW_BCTR()			(PPC_INST_BCTR)
> +#define PPC_RAW_BCTRL()			(PPC_INST_BCTRL)

Can you use the numeric value instead of the PPC_INST_BCTRL, to avoid conflict with 
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/4ca2bfdca2f47a293d05f61eb3c4e487ee170f1f.1621506159.git.christophe.leroy@xxxxxxxxxx/

>   #define PPC_RAW_MTCTR(r)		(PPC_INST_MTCTR | ___PPC_RT(r))
>   #define PPC_RAW_ADDI(d, a, i)		(PPC_INST_ADDI | ___PPC_RT(d) | ___PPC_RA(a) | IMM_L(i))
>   #define PPC_RAW_LI(r, i)		PPC_RAW_ADDI(r, 0, i)
> diff --git a/arch/powerpc/net/bpf_jit_comp32.c b/arch/powerpc/net/bpf_jit_comp32.c
> index bbb16099e8c7fa..40ab50bea61c02 100644
> --- a/arch/powerpc/net/bpf_jit_comp32.c
> +++ b/arch/powerpc/net/bpf_jit_comp32.c
> @@ -195,8 +195,8 @@ void bpf_jit_emit_func_call_rel(u32 *image, struct codegen_context *ctx, u64 fun
>   		/* Load function address into r0 */
>   		EMIT(PPC_RAW_LIS(__REG_R0, IMM_H(func)));
>   		EMIT(PPC_RAW_ORI(__REG_R0, __REG_R0, IMM_L(func)));
> -		EMIT(PPC_RAW_MTLR(__REG_R0));
> -		EMIT(PPC_RAW_BLRL());
> +		EMIT(PPC_RAW_MTCTR(__REG_R0));
> +		EMIT(PPC_RAW_BCTRL());
>   	}
>   }
>   
> diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
> index 57a8c1153851a0..ae9a6532be6ad4 100644
> --- a/arch/powerpc/net/bpf_jit_comp64.c
> +++ b/arch/powerpc/net/bpf_jit_comp64.c
> @@ -153,8 +153,8 @@ static void bpf_jit_emit_func_call_hlp(u32 *image, struct codegen_context *ctx,
>   	PPC_LI64(b2p[TMP_REG_2], func);
>   	/* Load actual entry point from function descriptor */
>   	PPC_BPF_LL(b2p[TMP_REG_1], b2p[TMP_REG_2], 0);
> -	/* ... and move it to LR */
> -	EMIT(PPC_RAW_MTLR(b2p[TMP_REG_1]));
> +	/* ... and move it to CTR */
> +	EMIT(PPC_RAW_MTCTR(b2p[TMP_REG_1]));
>   	/*
>   	 * Load TOC from function descriptor at offset 8.
>   	 * We can clobber r2 since we get called through a
> @@ -165,9 +165,9 @@ static void bpf_jit_emit_func_call_hlp(u32 *image, struct codegen_context *ctx,
>   #else
>   	/* We can clobber r12 */
>   	PPC_FUNC_ADDR(12, func);
> -	EMIT(PPC_RAW_MTLR(12));
> +	EMIT(PPC_RAW_MTCTR(12));
>   #endif
> -	EMIT(PPC_RAW_BLRL());
> +	EMIT(PPC_RAW_BCTRL());
>   }
>   
>   void bpf_jit_emit_func_call_rel(u32 *image, struct codegen_context *ctx, u64 func)
> @@ -202,8 +202,8 @@ void bpf_jit_emit_func_call_rel(u32 *image, struct codegen_context *ctx, u64 fun
>   	PPC_BPF_LL(12, 12, 0);
>   #endif
>   
> -	EMIT(PPC_RAW_MTLR(12));
> -	EMIT(PPC_RAW_BLRL());
> +	EMIT(PPC_RAW_MTCTR(12));
> +	EMIT(PPC_RAW_BCTRL());
>   }
>   
>   static void bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 out)
>
> base-commit: 112f47a1484ddca610b70cbe4a99f0d0f1701daf