[PATCH 10/17] powerpc/ftrace: Add separate ftrace_init_nop() with additional validation

[Christophe Leroy]

Le 19/06/2023 à 11:47, Naveen N Rao a écrit :
> Currently, we validate instructions around the ftrace location every
> time we have to enable/disable ftrace. Introduce ftrace_init_nop() to
> instead perform all the validation during ftrace initialization. This
> allows us to simply patch the necessary instructions during
> enabling/disabling ftrace.
> 
> Signed-off-by: Naveen N Rao <naveen at kernel.org>

Reviewed-by: Christophe Leroy <christophe.leroy at csgroup.eu>

> ---
>   arch/powerpc/include/asm/ftrace.h  |  6 +++
>   arch/powerpc/kernel/trace/ftrace.c | 71 ++++++++++++++++++++++++++++++
>   2 files changed, 77 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h
> index 702aaf2efa966c..ef9f0b97670d1c 100644
> --- a/arch/powerpc/include/asm/ftrace.h
> +++ b/arch/powerpc/include/asm/ftrace.h
> @@ -29,11 +29,17 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
>   unsigned long prepare_ftrace_return(unsigned long parent, unsigned long ip,
>   				    unsigned long sp);
>   
> +struct module;
> +struct dyn_ftrace;
>   struct dyn_arch_ftrace {
>   	struct module *mod;
>   };
>   
>   #ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS
> +#define ftrace_need_init_nop()	(true)
> +int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);
> +#define ftrace_init_nop ftrace_init_nop
> +
>   struct ftrace_regs {
>   	struct pt_regs regs;
>   };
> diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
> index 278bf8e52b6e89..98bd099c428ee0 100644
> --- a/arch/powerpc/kernel/trace/ftrace.c
> +++ b/arch/powerpc/kernel/trace/ftrace.c
> @@ -31,6 +31,16 @@
>   #define	NUM_FTRACE_TRAMPS	2
>   static unsigned long ftrace_tramps[NUM_FTRACE_TRAMPS];
>   
> +static ppc_inst_t ftrace_create_branch_inst(unsigned long ip, unsigned long addr, int link)
> +{
> +	ppc_inst_t op;
> +
> +	WARN_ON(!is_offset_in_branch_range(addr - ip));
> +	create_branch(&op, (u32 *)ip, addr, link ? BRANCH_SET_LINK : 0);
> +
> +	return op;
> +}
> +
>   static ppc_inst_t
>   ftrace_call_replace(unsigned long ip, unsigned long addr, int link)
>   {
> @@ -597,6 +607,67 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
>   }
>   #endif
>   
> +int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
> +{
> +	unsigned long addr, ip = rec->ip;
> +	ppc_inst_t old, new;
> +	int ret = 0;
> +
> +	/* Verify instructions surrounding the ftrace location */
> +	if (IS_ENABLED(CONFIG_PPC32)) {
> +		/* Expected sequence: 'mflr r0', 'stw r0,4(r1)', 'bl _mcount' */
> +		ret = ftrace_validate_inst(ip - 8, ppc_inst(PPC_RAW_MFLR(_R0)));
> +		if (!ret)
> +			ret = ftrace_validate_inst(ip - 4, ppc_inst(PPC_RAW_STW(_R0, _R1, 4)));
> +	} else if (IS_ENABLED(CONFIG_MPROFILE_KERNEL)) {
> +		/* Expected sequence: 'mflr r0', ['std r0,16(r1)'], 'bl _mcount' */
> +		ret = ftrace_read_inst(ip - 4, &old);
> +		if (!ret && !ppc_inst_equal(old, ppc_inst(PPC_RAW_MFLR(_R0)))) {
> +			ret = ftrace_validate_inst(ip - 8, ppc_inst(PPC_RAW_MFLR(_R0)));
> +			ret |= ftrace_validate_inst(ip - 4, ppc_inst(PPC_RAW_STD(_R0, _R1, 16)));
> +		}
> +	} else {
> +		return -EINVAL;
> +	}
> +
> +	if (ret)
> +		return ret;
> +
> +	if (!core_kernel_text(ip)) {
> +		if (!mod) {
> +			pr_err("0x%lx: No module provided for non-kernel address\n", ip);
> +			return -EFAULT;
> +		}
> +		rec->arch.mod = mod;
> +	}
> +
> +	/* Nop-out the ftrace location */
> +	new = ppc_inst(PPC_RAW_NOP());
> +	addr = MCOUNT_ADDR;
> +	if (is_offset_in_branch_range(addr - ip)) {
> +		/* Within range */
> +		old = ftrace_create_branch_inst(ip, addr, 1);
> +		ret = ftrace_modify_code(ip, old, new);
> +	} else if (core_kernel_text(ip) || (IS_ENABLED(CONFIG_MODULES) && mod)) {
> +		/*
> +		 * We would be branching to a linker-generated stub, or to the module _mcount
> +		 * stub. Let's just confirm we have a 'bl' here.
> +		 */
> +		ret = ftrace_read_inst(ip, &old);
> +		if (ret)
> +			return ret;
> +		if (!is_bl_op(old)) {
> +			pr_err("0x%lx: expected (bl) != found (%08lx)\n", ip, ppc_inst_as_ulong(old));
> +			return -EINVAL;
> +		}
> +		ret = patch_instruction((u32 *)ip, new);
> +	} else {
> +		return -EINVAL;
> +	}
> +
> +	return ret;
> +}
> +
>   int ftrace_update_ftrace_func(ftrace_func_t func)
>   {
>   	unsigned long ip = (unsigned long)(&ftrace_call);