[PATCH v4 3/5] RISC-V: fix jal addresses in patched alternatives

[Andrew Jones]

On Mon, Jan 09, 2023 at 07:17:53PM +0100, Heiko Stuebner wrote:
> From: Heiko Stuebner <heiko.stuebner at vrull.eu>
> 
> Alternatives live in a different section, so addresses used by jal
> instructions will point to wrong locations after the patch got applied.
> 
> Similar to arm64, adjust the location to consider that offset.
> 
> Signed-off-by: Heiko Stuebner <heiko.stuebner at vrull.eu>
> ---
>  arch/riscv/kernel/alternative.c | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/arch/riscv/kernel/alternative.c b/arch/riscv/kernel/alternative.c
> index 6212ea0eed72..985c284fe9f4 100644
> --- a/arch/riscv/kernel/alternative.c
> +++ b/arch/riscv/kernel/alternative.c
> @@ -79,6 +79,21 @@ static void riscv_alternative_fix_auipc_jalr(void *ptr, u32 auipc_insn,
>  	patch_text_nosync(ptr, call, sizeof(u32) * 2);
>  }
>  
> +static void riscv_alternative_fix_jal(void *ptr, u32 jal_insn, int patch_offset)
> +{
> +	s32 imm;
> +
> +	/* get and adjust new target address */
> +	imm = riscv_insn_extract_jtype_imm(jal_insn);
> +	imm -= patch_offset;
> +
> +	/* update instructions */

instruction

> +	riscv_insn_insert_jtype_imm(&jal_insn, imm);
> +
> +	/* patch the call place again */
> +	patch_text_nosync(ptr, &jal_insn, sizeof(u32));
> +}
> +
>  void riscv_alternative_fix_offsets(void *alt_ptr, unsigned int len,
>  				      int patch_offset)
>  {
> @@ -106,6 +121,18 @@ void riscv_alternative_fix_offsets(void *alt_ptr, unsigned int len,
>  			riscv_alternative_fix_auipc_jalr(alt_ptr + i * sizeof(u32),
>  							 insn, insn2, patch_offset);

I think we should add an i++ here. There's not a problem now, since we're
only adding a fixup for jal, not jalr, but we should future-proof this and
there's no reason to revisit an already fixed-up instruction anyway.

>  		}
> +
> +		if (riscv_insn_is_jal(insn)) {
> +			s32 imm = riscv_insn_extract_jtype_imm(insn);
> +
> +			/* don't modify jumps inside the alternative block */

Don't

> +			if ((alt_ptr + i * sizeof(u32) + imm) >= alt_ptr &&
> +			    (alt_ptr + i * sizeof(u32) + imm) < (alt_ptr + len))
> +				continue;
> +
> +			riscv_alternative_fix_jal(alt_ptr + i * sizeof(u32),
> +						  insn, patch_offset);
> +		}
>  	}
>  }
>  
> -- 
> 2.35.1
>

Otherwise

Reviewed-by: Andrew Jones <ajones at ventanamicro.com>

Thanks,
drew