Subject: Re: [PATCH v4 14/16] powerpc64: Add prefixed instructions to instruction data type

From: Alistair Popple <[email-masked]>
Date: Mon, 30 Mar 2020 20:05:12 +1100

<snip>

> @@ -487,12 +487,13 @@ int kprobe_post_handler(struct pt_regs *regs)
>  {
>  	struct kprobe *cur = kprobe_running();
>  	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> +	int len = ppc_inst_len(ppc_inst_read(cur->ainsn.insn));

I am no kprobes expert but it seems based on the code here that in some 
circumstances it's ok/expected that cur == NULL, therefore the assignment 
needs to happen after the check below to avoid dereferencing NULL. At least 
this was the problem I was hitting when running some of the kernel selftests.

- Alistair
 
>  	if (!cur || user_mode(regs))
>  		return 0;
> 
>  	/* make sure we got here for instruction we have a kprobe on */
> -	if (((unsigned long)cur->ainsn.insn + 4) != regs->nip)
> +	if ((unsigned long)cur->ainsn.insn + len != regs->nip)
>  		return 0;
> 
>  	if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
> @@ -501,7 +502,7 @@ int kprobe_post_handler(struct pt_regs *regs)
>  	}
> 
>  	/* Adjust nip to after the single-stepped instruction */
> -	regs->nip = (unsigned long)cur->addr + 4;
> +	regs->nip = (unsigned long)cur->addr + len;
>  	regs->msr |= kcb->kprobe_saved_msr;
> 
>  	/*Restore back the original saved kprobes variables and continue. */
> diff --git a/arch/powerpc/kernel/optprobes.c
> b/arch/powerpc/kernel/optprobes.c index 5b53c373373b..af6761859fba 100644
> --- a/arch/powerpc/kernel/optprobes.c
> +++ b/arch/powerpc/kernel/optprobes.c
> @@ -158,38 +158,38 @@ void patch_imm32_load_insns(unsigned int val,
> kprobe_opcode_t *addr)
> 
>  /*
>   * Generate instructions to load provided immediate 64-bit value
> - * to register 'r3' and patch these instructions at 'addr'.
> + * to register 'reg' and patch these instructions at 'addr'.
>   */
> -void patch_imm64_load_insns(unsigned long val, kprobe_opcode_t *addr)
> +void patch_imm64_load_insns(unsigned long val, int reg, kprobe_opcode_t
> *addr) {
> -	/* lis r3,(op)@highest */
> -	patch_instruction(addr, PPC_INST(PPC_INST_ADDIS | ___PPC_RT(3) |
> +	/* lis reg,(op)@highest */
> +	patch_instruction(addr, PPC_INST(PPC_INST_ADDIS | ___PPC_RT(reg) |
>  			  ((val >> 48) & 0xffff)));
>  	addr++;
> 
> -	/* ori r3,r3,(op)@higher */
> -	patch_instruction(addr, PPC_INST(PPC_INST_ORI | ___PPC_RA(3) |
> -			  ___PPC_RS(3) | ((val >> 32) & 0xffff)));
> +	/* ori reg,reg,(op)@higher */
> +	patch_instruction(addr, PPC_INST(PPC_INST_ORI | ___PPC_RA(reg) |
> +			  ___PPC_RS(reg) | ((val >> 32) & 0xffff)));
>  	addr++;
> 
> -	/* rldicr r3,r3,32,31 */
> -	patch_instruction(addr, PPC_INST(PPC_INST_RLDICR | ___PPC_RA(3) |
> -			  ___PPC_RS(3) | __PPC_SH64(32) | __PPC_ME64(31)));
> +	/* rldicr reg,reg,32,31 */
> +	patch_instruction(addr, PPC_INST(PPC_INST_RLDICR | ___PPC_RA(reg) |
> +			  ___PPC_RS(reg) | __PPC_SH64(32) | __PPC_ME64(31)));
>  	addr++;
> 
> -	/* oris r3,r3,(op)@h */
> -	patch_instruction(addr, PPC_INST(PPC_INST_ORIS | ___PPC_RA(3) |
> -			  ___PPC_RS(3) | ((val >> 16) & 0xffff)));
> +	/* oris reg,reg,(op)@h */
> +	patch_instruction(addr, PPC_INST(PPC_INST_ORIS | ___PPC_RA(reg) |
> +			  ___PPC_RS(reg) | ((val >> 16) & 0xffff)));
>  	addr++;
> 
> -	/* ori r3,r3,(op)@l */
> -	patch_instruction(addr, PPC_INST(PPC_INST_ORI | ___PPC_RA(3) |
> -			  ___PPC_RS(3) | (val & 0xffff)));
> +	/* ori reg,reg,(op)@l */
> +	patch_instruction(addr, PPC_INST(PPC_INST_ORI | ___PPC_RA(reg) |
> +			  ___PPC_RS(reg) | (val & 0xffff)));
>  }
> 
>  int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct
> kprobe *p) {
> -	ppc_inst branch_op_callback, branch_emulate_step;
> +	ppc_inst branch_op_callback, branch_emulate_step, temp;
>  	kprobe_opcode_t *op_callback_addr, *emulate_step_addr, *buff;
>  	long b_offset;
>  	unsigned long nip, size;
> @@ -239,7 +239,7 @@ int arch_prepare_optimized_kprobe(struct
> optimized_kprobe *op, struct kprobe *p) * Fixup the template with
> instructions to:
>  	 * 1. load the address of the actual probepoint
>  	 */
> -	patch_imm64_load_insns((unsigned long)op, buff + TMPL_OP_IDX);
> +	patch_imm64_load_insns((unsigned long)op, 3, buff + TMPL_OP_IDX);
> 
>  	/*
>  	 * 2. branch to optimized_callback() and emulate_step()
> @@ -268,7 +268,11 @@ int arch_prepare_optimized_kprobe(struct
> optimized_kprobe *op, struct kprobe *p) /*
>  	 * 3. load instruction to be emulated into relevant register, and
>  	 */
> -	patch_imm32_load_insns(*(unsigned int *)p->ainsn.insn, buff +
> TMPL_INSN_IDX); +	temp = ppc_inst_read(p->ainsn.insn);
> +	patch_imm64_load_insns(ppc_inst_word(temp) |
> +			       ((u64)ppc_inst_suffix(temp) << 32),
> +			       4,
> +			       buff + TMPL_INSN_IDX);
> 
>  	/*
>  	 * 4. branch back from trampoline
> diff --git a/arch/powerpc/kernel/optprobes_head.S
> b/arch/powerpc/kernel/optprobes_head.S index cf383520843f..ff8ba4d3824d
> 100644
> --- a/arch/powerpc/kernel/optprobes_head.S
> +++ b/arch/powerpc/kernel/optprobes_head.S
> @@ -94,6 +94,9 @@ optprobe_template_insn:
>  	/* 2, Pass instruction to be emulated in r4 */
>  	nop
>  	nop
> +	nop
> +	nop
> +	nop
> 
>  	.global optprobe_template_call_emulate
>  optprobe_template_call_emulate:
> diff --git a/arch/powerpc/kernel/trace/ftrace.c
> b/arch/powerpc/kernel/trace/ftrace.c index ad451205f268..3b8655f57b4a
> 100644
> --- a/arch/powerpc/kernel/trace/ftrace.c
> +++ b/arch/powerpc/kernel/trace/ftrace.c
> @@ -42,9 +42,24 @@
>  static unsigned long ftrace_tramps[NUM_FTRACE_TRAMPS];
> 
>  static long
> -read_inst(ppc_inst *inst, const void *src)
> +read_inst(ppc_inst *p, const void *src)
>  {
> -	return probe_kernel_read((void *)inst, src, MCOUNT_INSN_SIZE);
> +	ppc_inst inst;
> +	long err;
> +
> +	err = probe_kernel_read((void *)&inst.prefix,
> +				src, MCOUNT_INSN_SIZE);
> +	if (err)
> +		return err;
> +
> +	if (ppc_inst_prefixed(inst))
> +		err = probe_kernel_read((void *)&inst.suffix,
> +					src + 4, MCOUNT_INSN_SIZE);
> +	if (err)
> +		return err;
> +
> +	ppc_inst_write(p, inst);
> +	return 0;
>  }
> 
>  static ppc_inst
> diff --git a/arch/powerpc/kernel/uprobes.c b/arch/powerpc/kernel/uprobes.c
> index d1dff1dc3a11..3e4fbb5c1b1e 100644
> --- a/arch/powerpc/kernel/uprobes.c
> +++ b/arch/powerpc/kernel/uprobes.c
> @@ -111,7 +111,7 @@ int arch_uprobe_post_xol(struct arch_uprobe *auprobe,
> struct pt_regs *regs) * support doesn't exist and have to fix-up the next
> instruction * to be executed.
>  	 */
> -	regs->nip = utask->vaddr + MAX_UINSN_BYTES;
> +	regs->nip = utask->vaddr + ppc_inst_len(ppc_inst_read(auprobe->insn));
> 
>  	user_disable_single_step(current);
>  	return 0;
> diff --git a/arch/powerpc/lib/code-patching.c
> b/arch/powerpc/lib/code-patching.c index fa7f32adf029..3b8277a64b8f 100644
> --- a/arch/powerpc/lib/code-patching.c
> +++ b/arch/powerpc/lib/code-patching.c
> @@ -24,17 +24,27 @@ static int __patch_instruction(ppc_inst *exec_addr,
> ppc_inst instr, {
>  	int err = 0;
> 
> -	__put_user_asm(instr, patch_addr, err, "stw");
> +	__put_user_asm(ppc_inst_word(instr), patch_addr, err, "stw");
>  	if (err)
>  		return err;
> 
>  	asm ("dcbst 0, %0; sync; icbi 0,%1; sync; isync" :: "r" (patch_addr),
>  							    "r" (exec_addr));
> 
> +	if (!ppc_inst_prefixed(instr))
> +		return 0;
> +
> +	__put_user_asm(ppc_inst_suffix(instr), patch_addr + 4, err, "stw");
> +	if (err)
> +		return err;
> +
> +	asm ("dcbst 0, %0; sync; icbi 0,%1; sync; isync" :: "r" (patch_addr + 4),
> +							    "r" (exec_addr + 4));
> +
>  	return 0;
>  }
> 
> -int raw_patch_instruction(ppc_inst *addr, ppc_inst instr)
> +int raw_patch_instruction(void *addr, ppc_inst instr)
>  {
>  	return __patch_instruction(addr, instr, addr);
>  }
> @@ -184,7 +194,7 @@ static int do_patch_instruction(ppc_inst *addr, ppc_inst
> instr)
> 
>  #endif /* CONFIG_STRICT_KERNEL_RWX */
> 
> -int patch_instruction(unsigned int *addr, unsigned int instr)
> +int patch_instruction(void *addr, ppc_inst instr)
>  {
>  	/* Make sure we aren't patching a freed init section */
>  	if (init_mem_is_free && init_section_contains(addr, 4)) {
> @@ -195,7 +205,7 @@ int patch_instruction(unsigned int *addr, unsigned int
> instr) }
>  NOKPROBE_SYMBOL(patch_instruction);
> 
> -int patch_branch(ppc_inst *addr, unsigned long target, int flags)
> +int patch_branch(void *addr, unsigned long target, int flags)
>  {
>  	return patch_instruction(addr, create_branch(addr, target, flags));
>  }
> @@ -264,7 +274,7 @@ ppc_inst create_branch(const ppc_inst *addr,
>  	return instruction;
>  }
> 
> -unsigned int create_cond_branch(const unsigned int *addr,
> +ppc_inst create_cond_branch(const void *addr,
>  				unsigned long target, int flags)
>  {
>  	ppc_inst instruction;
> @@ -344,7 +354,7 @@ static unsigned long branch_bform_target(const ppc_inst
> *instr) return (unsigned long)imm;
>  }
> 
> -unsigned long branch_target(const ppc_inst *instr)
> +unsigned long branch_target(const void *instr)
>  {
>  	if (instr_is_branch_iform(ppc_inst_read(instr)))
>  		return branch_iform_target(instr);
> diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
> index bae878a83fa5..ab4c71c43c8c 100644
> --- a/arch/powerpc/lib/sstep.c
> +++ b/arch/powerpc/lib/sstep.c
> @@ -1169,10 +1169,12 @@ int analyse_instr(struct instruction_op *op, const
> struct pt_regs *regs, unsigned long int imm;
>  	unsigned long int val, val2;
>  	unsigned int mb, me, sh;
> -	unsigned int word;
> +	unsigned int word, suffix;
>  	long ival;
> 
>  	word = ppc_inst_word(instr);
> +	suffix = ppc_inst_suffix(instr);
> +
>  	op->type = COMPUTE;
> 
>  	opcode = word >> 26;
> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> index ee084411f2f5..c5536e1a3356 100644
> --- a/arch/powerpc/xmon/xmon.c
> +++ b/arch/powerpc/xmon/xmon.c
> @@ -110,7 +110,7 @@ struct bpt {
>  #define BP_DABR		4
> 
>  #define NBPTS	256
> -#define BPT_WORDS	2
> +#define BPT_WORDS	4
>  static struct bpt bpts[NBPTS];
>  static struct bpt dabr;
>  static struct bpt *iabr;
> @@ -118,12 +118,13 @@ static unsigned bpinstr = 0x7fe00008;	/* trap */
> 
>  #define BP_NUM(bp)	((bp) - bpts + 1)
> 
> -static unsigned int __section(.text.xmon_bpts) bpt_table[NBPTS *
> BPT_WORDS]; +static unsigned int __section(.text.xmon_bpts) bpt_table[NBPTS
> * BPT_WORDS] __aligned(64);
> 
>  /* Prototypes */
>  static int cmds(struct pt_regs *);
>  static int mread(unsigned long, void *, int);
>  static int mwrite(unsigned long, void *, int);
> +static int mread_instr(unsigned long, ppc_inst *);
>  static int handle_fault(struct pt_regs *);
>  static void byterev(unsigned char *, int);
>  static void memex(void);
> @@ -759,8 +760,8 @@ static int xmon_bpt(struct pt_regs *regs)
> 
>  	/* Are we at the trap at bp->instr[1] for some bp? */
>  	bp = in_breakpoint_table(regs->nip, &offset);
> -	if (bp != NULL && offset == 4) {
> -		regs->nip = bp->address + 4;
> +	if (bp != NULL && (offset == 4 || offset == 8)) {
> +		regs->nip = bp->address + offset;
>  		atomic_dec(&bp->ref_count);
>  		return 1;
>  	}
> @@ -862,7 +863,7 @@ static struct bpt *in_breakpoint_table(unsigned long
> nip, unsigned long *offp) if (off >= sizeof(bpt_table))
>  		return NULL;
>  	bp_off = off % (sizeof(unsigned int) * BPT_WORDS);
> -	if (bp_off != 0 && bp_off != 4)
> +	if (bp_off != 0 && bp_off != 4 && bp_off != 8)
>  		return NULL;
>  	*offp = bp_off;
>  	return bpts + ((off - bp_off) / (sizeof(unsigned int) * BPT_WORDS));
> @@ -881,7 +882,6 @@ static struct bpt *new_breakpoint(unsigned long a)
>  		if (!bp->enabled && atomic_read(&bp->ref_count) == 0) {
>  			bp->address = a;
>  			bp->instr = bpt_table + ((bp - bpts) * BPT_WORDS);
> -			patch_instruction(bp->instr + 1, PPC_INST(bpinstr));
>  			return bp;
>  		}
>  	}
> @@ -900,7 +900,7 @@ static void insert_bpts(void)
>  	for (i = 0; i < NBPTS; ++i, ++bp) {
>  		if ((bp->enabled & (BP_TRAP|BP_CIABR)) == 0)
>  			continue;
> -		if (mread(bp->address, &instr, 4) != 4) {
> +		if (!mread_instr(bp->address, &instr)) {
>  			printf("Couldn't read instruction at %lx, "
>  			       "disabling breakpoint there\n", bp->address);
>  			bp->enabled = 0;
> @@ -913,9 +913,10 @@ static void insert_bpts(void)
>  			continue;
>  		}
>  		patch_instruction(bp->instr, instr);
> +		patch_instruction(bp->instr + ppc_inst_len(instr), PPC_INST(bpinstr));
>  		if (bp->enabled & BP_CIABR)
>  			continue;
> -		if (patch_instruction((ppc_inst *)bp->address,
> +		if (patch_instruction((void *)bp->address,
>  							PPC_INST(bpinstr)) != 0) {
>  			printf("Couldn't write instruction at %lx, "
>  			       "disabling breakpoint there\n", bp->address);
> @@ -950,7 +951,7 @@ static void remove_bpts(void)
>  	for (i = 0; i < NBPTS; ++i, ++bp) {
>  		if ((bp->enabled & (BP_TRAP|BP_CIABR)) != BP_TRAP)
>  			continue;
> -		if (mread(bp->address, &instr, 4) == 4
> +		if (mread_instr(bp->address, &instr)
>  		    && ppc_inst_equal(instr, PPC_INST(bpinstr))
>  		    && patch_instruction(
>  			(ppc_inst *)bp->address, ppc_inst_read(bp->instr)) != 0)
> @@ -1166,7 +1167,7 @@ static int do_step(struct pt_regs *regs)
>  	force_enable_xmon();
>  	/* check we are in 64-bit kernel mode, translation enabled */
>  	if ((regs->msr & (MSR_64BIT|MSR_PR|MSR_IR)) == (MSR_64BIT|MSR_IR)) {
> -		if (mread(regs->nip, &instr, 4) == 4) {
> +		if (mread_instr(regs->nip, &instr)) {
>  			stepped = emulate_step(regs, instr);
>  			if (stepped < 0) {
>  				printf("Couldn't single-step %s instruction\n",
> @@ -1333,7 +1334,7 @@ static long check_bp_loc(unsigned long addr)
>  		printf("Breakpoints may only be placed at kernel addresses\n");
>  		return 0;
>  	}
> -	if (!mread(addr, &instr, sizeof(instr))) {
> +	if (!mread_instr(addr, &instr)) {
>  		printf("Can't read instruction at address %lx\n", addr);
>  		return 0;
>  	}
> @@ -2126,6 +2127,21 @@ mwrite(unsigned long adrs, void *buf, int size)
>  	return n;
>  }
> 
> +static int
> +mread_instr(unsigned long adrs, ppc_inst *instr)
> +{
> +	if (setjmp(bus_error_jmp) == 0) {
> +		catch_memory_errors = 1;
> +		sync();
> +		*instr = ppc_inst_read((void *)adrs);
> +		sync();
> +		/* wait a little while to see if we get a machine check */
> +		__delay(200);
> +	}
> +	catch_memory_errors = 0;
> +	return ppc_inst_len(*instr);
> +}
> +
>  static int fault_type;
>  static int fault_except;
>  static char *fault_chars[] = { "--", "**", "##" };