Messages in this thread Patch in this message | | | Date | Tue, 1 Mar 2022 00:25:13 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 15/39] x86/ibt,kprobes: Fix more +0 assumptions |
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On Mon, Feb 28, 2022 at 03:07:05PM +0900, Masami Hiramatsu wrote: > Hi Peter, > > So, instead of this change, can you try below? > This introduce the arch_adjust_kprobe_addr() and use it in the kprobe_addr() > so that it can handle the case that user passed the probe address in > _text+OFFSET format.
It works a little... at the very least it still needs arch_kprobe_on_func_entry() allowing offset 4.
But looking at this, we've got:
kprobe_on_func_entry(addr, sym, offset) _kprobe_addr(addr, sym, offset) if (sym) addr = kprobe_lookup_name() = kallsyms_lookup_name() arch_adjust_kprobe_addr(addr+offset) skip_endbr() kallsyms_loopup_size_offset(addr, ...) kallsyms_lookup_size_offset(addr, NULL, &offset) arch_kprobe_on_func_entry(offset)
Which is _3_ kallsyms lookups and 3 weak/arch hooks.
Surely we can make this a little more streamlined? The below seems to work.
I think with a little care and testing it should be possible to fold all the magic of PowerPC's kprobe_lookup_name() into this one hook as well, meaning we can get rid of kprobe_lookup_name() entirely. Naveen?
This then gets us down to a 1 kallsyms call and 1 arch hook. Hmm?
--- arch/powerpc/kernel/kprobes.c | 34 +++++++++++++++--------- arch/x86/kernel/kprobes/core.c | 17 ++++++++++++ include/linux/kprobes.h | 3 +- kernel/kprobes.c | 56 ++++++++++++++++++++++++++++++++++------- 4 files changed, 87 insertions(+), 23 deletions(-)
--- a/arch/powerpc/kernel/kprobes.c +++ b/arch/powerpc/kernel/kprobes.c @@ -105,6 +105,27 @@ kprobe_opcode_t *kprobe_lookup_name(cons return addr; } +static bool arch_kprobe_on_func_entry(unsigned long offset) +{ +#ifdef PPC64_ELF_ABI_v2 +#ifdef CONFIG_KPROBES_ON_FTRACE + return offset <= 16; +#else + return offset <= 8; +#endif +#else + return !offset; +#endif +} + +/* XXX try and fold the magic of kprobe_lookup_name() in this */ +kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr, unsigned long offset, + bool *on_func_entry) +{ + *on_func_entry = arch_kprobe_on_func_entry(offset); + return (kprobe_opcode_t *)(addr + offset); +} + void *alloc_insn_page(void) { void *page; @@ -218,19 +239,6 @@ static nokprobe_inline void set_current_ kcb->kprobe_saved_msr = regs->msr; } -bool arch_kprobe_on_func_entry(unsigned long offset) -{ -#ifdef PPC64_ELF_ABI_v2 -#ifdef CONFIG_KPROBES_ON_FTRACE - return offset <= 16; -#else - return offset <= 8; -#endif -#else - return !offset; -#endif -} - void arch_prepare_kretprobe(struct kretprobe_instance *ri, struct pt_regs *regs) { ri->ret_addr = (kprobe_opcode_t *)regs->link; --- a/arch/x86/kernel/kprobes/core.c +++ b/arch/x86/kernel/kprobes/core.c @@ -52,6 +52,7 @@ #include <asm/insn.h> #include <asm/debugreg.h> #include <asm/set_memory.h> +#include <asm/ibt.h> #include "common.h" @@ -301,6 +302,22 @@ static int can_probe(unsigned long paddr return (addr == paddr); } +/* If the x86 support IBT (ENDBR) it must be skipped. */ +kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr, unsigned long offset, + bool *on_func_entry) +{ + if (is_endbr(*(u32 *)addr)) { + *on_func_entry = !offset || offset == 4; + if (*on_func_entry) + offset = 4; + + } else { + *on_func_entry = !offset; + } + + return (kprobe_opcode_t *)(addr + offset); +} + /* * Copy an instruction with recovering modified instruction by kprobes * and adjust the displacement if the instruction uses the %rip-relative --- a/include/linux/kprobes.h +++ b/include/linux/kprobes.h @@ -265,7 +265,6 @@ extern int arch_init_kprobes(void); extern void kprobes_inc_nmissed_count(struct kprobe *p); extern bool arch_within_kprobe_blacklist(unsigned long addr); extern int arch_populate_kprobe_blacklist(void); -extern bool arch_kprobe_on_func_entry(unsigned long offset); extern int kprobe_on_func_entry(kprobe_opcode_t *addr, const char *sym, unsigned long offset); extern bool within_kprobe_blacklist(unsigned long addr); @@ -384,6 +383,8 @@ static inline struct kprobe_ctlblk *get_ } kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset); +kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr, unsigned long offset, bool *on_func_entry); + int register_kprobe(struct kprobe *p); void unregister_kprobe(struct kprobe *p); int register_kprobes(struct kprobe **kps, int num); --- a/kernel/kprobes.c +++ b/kernel/kprobes.c @@ -1489,24 +1489,63 @@ bool within_kprobe_blacklist(unsigned lo } /* + * arch_adjust_kprobe_addr - adjust the address + * @addr: symbol base address + * @offset: offset within the symbol + * @on_func_entry: was this @addr+@offset on the function entry + * + * Typically returns @addr + @offset, except for special cases where the + * function might be prefixed by a CFI landing pad, in that case any offset + * inside the landing pad is mapped to the first 'real' instruction of the + * symbol. + * + * Specifically, for things like IBT/BTI, skip the resp. ENDBR/BTI.C + * instruction at +0. + */ +kprobe_opcode_t *__weak arch_adjust_kprobe_addr(unsigned long addr, + unsigned long offset, + bool *on_func_entry) +{ + *on_func_entry = !offset; + return (kprobe_opcode_t *)(addr + offset); +} + +/* * If 'symbol_name' is specified, look it up and add the 'offset' * to it. This way, we can specify a relative address to a symbol. * This returns encoded errors if it fails to look up symbol or invalid * combination of parameters. */ -static kprobe_opcode_t *_kprobe_addr(kprobe_opcode_t *addr, - const char *symbol_name, unsigned int offset) +static kprobe_opcode_t * +_kprobe_addr(kprobe_opcode_t *addr, const char *symbol_name, + unsigned long offset, bool *on_func_entry) { if ((symbol_name && addr) || (!symbol_name && !addr)) goto invalid; if (symbol_name) { + /* + * Input: @sym + @offset + * Output: @addr + @offset + * + * NOTE: kprobe_lookup_name() does *NOT* fold the offset + * argument into it's output! + */ addr = kprobe_lookup_name(symbol_name, offset); if (!addr) return ERR_PTR(-ENOENT); + } else { + /* + * Input: @addr + @offset + * Output: @addr' + @offset' + */ + if (!kallsyms_lookup_size_offset((unsigned long)addr + offset, + NULL, &offset)) + return ERR_PTR(-ENOENT); + addr = (kprobe_opcode_t *)((unsigned long)addr - offset); } - addr = (kprobe_opcode_t *)(((char *)addr) + offset); + addr = arch_adjust_kprobe_addr((unsigned long)addr, offset, on_func_entry); if (addr) return addr; @@ -1516,7 +1555,8 @@ static kprobe_opcode_t *_kprobe_addr(kpr static kprobe_opcode_t *kprobe_addr(struct kprobe *p) { - return _kprobe_addr(p->addr, p->symbol_name, p->offset); + bool on_func_entry; + return _kprobe_addr(p->addr, p->symbol_name, p->offset, &on_func_entry); } /* @@ -2067,15 +2107,13 @@ bool __weak arch_kprobe_on_func_entry(un */ int kprobe_on_func_entry(kprobe_opcode_t *addr, const char *sym, unsigned long offset) { - kprobe_opcode_t *kp_addr = _kprobe_addr(addr, sym, offset); + bool on_func_entry; + kprobe_opcode_t *kp_addr = _kprobe_addr(addr, sym, offset, &on_func_entry); if (IS_ERR(kp_addr)) return PTR_ERR(kp_addr); - if (!kallsyms_lookup_size_offset((unsigned long)kp_addr, NULL, &offset)) - return -ENOENT; - - if (!arch_kprobe_on_func_entry(offset)) + if (!on_func_entry) return -EINVAL; return 0;
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