Re: [PATCH] riscv: ftrace: Fix to pass correct ftrace_regs to ftrace_func_t functions

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

Hi,

Gentry ping.

I think this should be an important fix because if a fprobe handler without
FTRACE_OPS_FL_SAVE_REGS tries to access any register via ftrace_regs, that
will get a wrong value.

Thank you,

On Mon,  2 Oct 2023 21:50:34 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:

> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> 
> Since ftrace_func_t requires to pass 'struct ftrace_regs *' as the 4th
> argument even if FTRACE_OPS_FL_SAVE_REGS is not set, ftrace_caller must
> pass 'struct ftrace_regs *', which is a partial pt_regs, on the stack
> to the ftrace_func_t functions, so that the ftrace_func_t functions can
> access some partial registers.
> 
> Fix to allocate 'struct ftrace_regs' (which has the same size of 'struct
> pt_regs') on the stack and save partial (argument) registers on it
> instead of reduced size custom data structure.
> 
> Fixes: afc76b8b8011 ("riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> ---
>  arch/riscv/kernel/mcount-dyn.S |   65 +++++++++++++++++-----------------------
>  1 file changed, 28 insertions(+), 37 deletions(-)
> 
> diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
> index 669b8697aa38..84963680eff4 100644
> --- a/arch/riscv/kernel/mcount-dyn.S
> +++ b/arch/riscv/kernel/mcount-dyn.S
> @@ -14,46 +14,37 @@
>  	.text
>  
>  #define FENTRY_RA_OFFSET	8
> -#define ABI_SIZE_ON_STACK	80
> -#define ABI_A0			0
> -#define ABI_A1			8
> -#define ABI_A2			16
> -#define ABI_A3			24
> -#define ABI_A4			32
> -#define ABI_A5			40
> -#define ABI_A6			48
> -#define ABI_A7			56
> -#define ABI_T0			64
> -#define ABI_RA			72
>  
>  	.macro SAVE_ABI
> -	addi	sp, sp, -ABI_SIZE_ON_STACK
> -
> -	REG_S	a0, ABI_A0(sp)
> -	REG_S	a1, ABI_A1(sp)
> -	REG_S	a2, ABI_A2(sp)
> -	REG_S	a3, ABI_A3(sp)
> -	REG_S	a4, ABI_A4(sp)
> -	REG_S	a5, ABI_A5(sp)
> -	REG_S	a6, ABI_A6(sp)
> -	REG_S	a7, ABI_A7(sp)
> -	REG_S	t0, ABI_T0(sp)
> -	REG_S	ra, ABI_RA(sp)
> +	addi	sp, sp, -PT_SIZE_ON_STACK
> +
> +	/* Save t0 as epc for ftrace_regs_get_instruction_pointer() */
> +	REG_S	t0, PT_EPC(sp)
> +	REG_S	a0, PT_A0(sp)
> +	REG_S	a1, PT_A1(sp)
> +	REG_S	a2, PT_A2(sp)
> +	REG_S	a3, PT_A3(sp)
> +	REG_S	a4, PT_A4(sp)
> +	REG_S	a5, PT_A5(sp)
> +	REG_S	a6, PT_A6(sp)
> +	REG_S	a7, PT_A7(sp)
> +	REG_S	t0, PT_T0(sp)
> +	REG_S	ra, PT_RA(sp)
>  	.endm
>  
>  	.macro RESTORE_ABI
> -	REG_L	a0, ABI_A0(sp)
> -	REG_L	a1, ABI_A1(sp)
> -	REG_L	a2, ABI_A2(sp)
> -	REG_L	a3, ABI_A3(sp)
> -	REG_L	a4, ABI_A4(sp)
> -	REG_L	a5, ABI_A5(sp)
> -	REG_L	a6, ABI_A6(sp)
> -	REG_L	a7, ABI_A7(sp)
> -	REG_L	t0, ABI_T0(sp)
> -	REG_L	ra, ABI_RA(sp)
> -
> -	addi	sp, sp, ABI_SIZE_ON_STACK
> +	REG_L	a0, PT_A0(sp)
> +	REG_L	a1, PT_A1(sp)
> +	REG_L	a2, PT_A2(sp)
> +	REG_L	a3, PT_A3(sp)
> +	REG_L	a4, PT_A4(sp)
> +	REG_L	a5, PT_A5(sp)
> +	REG_L	a6, PT_A6(sp)
> +	REG_L	a7, PT_A7(sp)
> +	REG_L	t0, PT_T0(sp)
> +	REG_L	ra, PT_RA(sp)
> +
> +	addi	sp, sp, PT_SIZE_ON_STACK
>  	.endm
>  
>  #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> @@ -96,8 +87,8 @@ ftrace_call:
>  	call	ftrace_stub
>  
>  #ifdef CONFIG_FUNCTION_GRAPH_TRACER
> -	addi	a0, sp, ABI_RA
> -	REG_L	a1, ABI_T0(sp)
> +	addi	a0, sp, PT_RA
> +	REG_L	a1, PT_T0(sp)
>  	addi	a1, a1, -FENTRY_RA_OFFSET
>  #ifdef HAVE_FUNCTION_GRAPH_FP_TEST
>  	mv	a2, s0
> 
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>