[kernel-hardening] Re: [PATCH V11 4/5] vsprintf: add printk specifier %px

[Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>]

Hello,

On (12/05/17 13:22), Linus Torvalds wrote:
[..]
> It's not like those hex numbers were really helping people anyway.
> We've turned off most of them on x86 oops reports long ago (and
> entirely independently of the pointer hashing). Having stared at a lot
> of oopses in my time, the only hex numbers that tend to be really
> relevant are (a) the register contents (which aren't %p anyway), and
> things like the faulting address (which is not, and never has been, %p
> on x86, but might be on some other architecture).

I see some %p-s being used in _supposedly_ important output,
like arch/x86/mm/fault.c

show_fault_oops(struct pt_regs *regs, unsigned long error_code,
		unsigned long address)
...
	printk(KERN_CONT " at %p\n", (void *) address);
	printk(KERN_ALERT "IP: %pS\n", (void *)regs->ip);


a quick %p grep gives me the following list:

arch/arm/mm/fault.c:    pr_alert("pgd = %p\n", mm->pgd);
arch/arm64/mm/fault.c:  pr_alert("%s pgtable: %luk pages, %u-bit VAs, pgd = %p\n",
arch/arm64/mm/fault.c:          pr_info_ratelimited("%s[%d]: %s exception: pc=%p sp=%p\n",
arch/m68k/mm/fault.c:   pr_debug("send_fault_sig: %p,%d,%d\n", siginfo.si_addr,
arch/m68k/mm/fault.c:           pr_cont(" at virtual address %p\n", siginfo.si_addr);
arch/m68k/mm/fault.c:   pr_debug("do page fault:\nregs->sr=%#x, regs->pc=%#lx, address=%#lx, %ld, %p\n",
arch/microblaze/mm/fault.c:             pr_emerg("Page fault in user mode with faulthandler_disabled(), mm = %p\n",
arch/mn10300/mm/fault.c:        printk(KERN_DEBUG "pgd entry %p: %016Lx\n",
arch/mn10300/mm/fault.c:        printk(KERN_DEBUG "pmd entry %p: %016Lx\n",
arch/mn10300/mm/fault.c:        printk(KERN_DEBUG "pte entry %p: %016Lx\n",
arch/mn10300/mm/fault.c:        printk(KERN_DEBUG "--- do_page_fault(%p,%s:%04lx,%08lx)\n",
arch/powerpc/mm/fault.c:                                           " mm=%p\n",
arch/sh/mm/fault.c:     printk(KERN_ALERT "pgd = %p\n", pgd);
arch/unicore32/mm/fault.c:      printk(KERN_ALERT "pgd = %p\n", mm->pgd);
arch/x86/mm/fault.c:    printk(KERN_CONT " at %p\n", (void *) address);
arch/x86/mm/fault.c:    printk(KERN_ALERT "IP: %pS\n", (void *)regs->ip);
arch/x86/mm/fault.c:    printk("%s%s[%d]: segfault at %lx ip %p sp %p error %lx",


or is it OK to show hashes instead of pgd or pmd pointers?

	-ss