Re: [PATCH v2 10/13] RISC-V: fix auipc-jalr addresses in patched alternatives

From: Conor Dooley <conor@kernel.org>
To: Heiko Stuebner <heiko@sntech.de>
Cc: linux-riscv@lists.infradead.org, palmer@dabbelt.com,
	christoph.muellner@vrull.eu, prabhakar.csengg@gmail.com,
	philipp.tomsich@vrull.eu, ajones@ventanamicro.com,
	emil.renner.berthing@canonical.com,
	Heiko Stuebner <heiko.stuebner@vrull.eu>
Subject: Re: [PATCH v2 10/13] RISC-V: fix auipc-jalr addresses in patched alternatives
Date: Wed, 30 Nov 2022 16:37:42 +0000	[thread overview]
Message-ID: <Y4eG1vwwjKIMx7gs@spud> (raw)
In-Reply-To: <20221128102632.435174-11-heiko@sntech.de>

On Mon, Nov 28, 2022 at 11:26:29AM +0100, Heiko Stuebner wrote:
> From: Heiko Stuebner <heiko.stuebner@vrull.eu>
> 
> Alternatives live in a different section, so addresses used by call
> functions 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@vrull.eu>

This looks like an improved version of what I gave an R-b for last time?
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>

> ---
>  arch/riscv/include/asm/alternative.h |  3 ++
>  arch/riscv/kernel/alternative.c      | 72 ++++++++++++++++++++++++++++
>  arch/riscv/kernel/cpufeature.c       | 11 ++++-
>  3 files changed, 84 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/alternative.h b/arch/riscv/include/asm/alternative.h
> index 6511dd73e812..c58ec3cc4bc3 100644
> --- a/arch/riscv/include/asm/alternative.h
> +++ b/arch/riscv/include/asm/alternative.h
> @@ -27,6 +27,9 @@ void __init apply_boot_alternatives(void);
>  void __init apply_early_boot_alternatives(void);
>  void apply_module_alternatives(void *start, size_t length);
>  
> +void riscv_alternative_fix_auipc_jalr(void *alt_ptr, unsigned int len,
> +				      int patch_offset);
> +
>  struct alt_entry {
>  	void *old_ptr;		 /* address of original instruciton or data  */
>  	void *alt_ptr;		 /* address of replacement instruction or data */
> diff --git a/arch/riscv/kernel/alternative.c b/arch/riscv/kernel/alternative.c
> index a7d26a00beea..292cc42dc3be 100644
> --- a/arch/riscv/kernel/alternative.c
> +++ b/arch/riscv/kernel/alternative.c
> @@ -15,6 +15,8 @@
>  #include <asm/vendorid_list.h>
>  #include <asm/sbi.h>
>  #include <asm/csr.h>
> +#include <asm/insn.h>
> +#include <asm/patch.h>
>  
>  struct cpu_manufacturer_info_t {
>  	unsigned long vendor_id;
> @@ -53,6 +55,76 @@ static void __init_or_module riscv_fill_cpu_mfr_info(struct cpu_manufacturer_inf
>  	}
>  }
>  
> +static unsigned int riscv_instruction_at(void *p, unsigned int offset)
> +{
> +	u16 *parcel = p + (offset * sizeof(u32));
> +
> +	return (unsigned int)parcel[0] | (unsigned int)parcel[1] << 16;
> +}
> +
> +static inline bool riscv_insn_is_auipc_jalr(u32 insn1, u32 insn2)
> +{
> +	return riscv_insn_is_auipc(insn1) && riscv_insn_is_jalr(insn2);
> +}
> +
> +#define JALR_SIGN_MASK		BIT(RV_I_IMM_SIGN_OPOFF - RV_I_IMM_11_0_OPOFF)
> +#define AUIPC_PAD		(0x00001000)
> +
> +#define to_jalr_imm(value)						\
> +	((value & RV_I_IMM_11_0_MASK) << RV_I_IMM_11_0_OPOFF)
> +
> +#define to_auipc_imm(value)						\
> +	((value & JALR_SIGN_MASK) ?					\
> +	((value & RV_U_IMM_31_12_MASK) + AUIPC_PAD) :	\
> +	(value & RV_U_IMM_31_12_MASK))
> +
> +void riscv_alternative_fix_auipc_jalr(void *alt_ptr, unsigned int len,
> +				      int patch_offset)
> +{
> +	int num_instr = len / sizeof(u32);
> +	unsigned int call[2];
> +	int i;
> +	int imm;
> +	u32 rd1;
> +
> +	/*
> +	 * stop one instruction before the end, as we're checking
> +	 * for auipc + jalr
> +	 */
> +	for (i = 0; i < num_instr - 1; i++) {
> +		u32 inst1 = riscv_instruction_at(alt_ptr, i);
> +		u32 inst2 = riscv_instruction_at(alt_ptr, i + 1);
> +
> +		if (!riscv_insn_is_auipc_jalr(inst1, inst2))
> +			continue;
> +
> +		/* call will use ra register */
> +		rd1 = RV_EXTRACT_RD_REG(inst1);
> +		if (rd1 != 1)
> +			continue;
> +
> +		/* get and adjust new target address */
> +		imm = RV_EXTRACT_UTYPE_IMM(inst1);
> +		imm += RV_EXTRACT_ITYPE_IMM(inst2);
> +		imm -= patch_offset;
> +
> +		/* pick the original auipc + jalr */
> +		call[0] = inst1;
> +		call[1] = inst2;
> +
> +		/* drop the old IMMs */
> +		call[0] &= ~(RV_U_IMM_31_12_MASK);
> +		call[1] &= ~(RV_I_IMM_11_0_MASK << RV_I_IMM_11_0_OPOFF);
> +
> +		/* add the adapted IMMs */
> +		call[0] |= to_auipc_imm(imm);
> +		call[1] |= to_jalr_imm(imm);
> +
> +		/* patch the call place again */
> +		patch_text_nosync(alt_ptr + i * sizeof(u32), call, 8);
> +	}
> +}
> +
>  /*
>   * This is called very early in the boot process (directly after we run
>   * a feature detect on the boot CPU). No need to worry about other CPUs
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 694267d1fe81..ba62a4ff5ccd 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -316,8 +316,15 @@ void __init_or_module riscv_cpufeature_patch_func(struct alt_entry *begin,
>  		}
>  
>  		tmp = (1U << alt->errata_id);
> -		if (cpu_req_feature & tmp)
> -			patch_text_nosync(alt->old_ptr, alt->alt_ptr, alt->alt_len);
> +		if (cpu_req_feature & tmp) {
> +			/* do the basic patching */
> +			patch_text_nosync(alt->old_ptr, alt->alt_ptr,
> +					  alt->alt_len);
> +
> +			riscv_alternative_fix_auipc_jalr(alt->old_ptr,
> +							 alt->alt_len,
> +							 alt->old_ptr - alt->alt_ptr);
> +		}
>  	}
>  }
>  #endif
> -- 
> 2.35.1
> 
> 
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