Adding Kees and Linus in Cc because it modifies %pK behavior.
On Thu 2022-01-27 11:11:02, Christophe Leroy wrote:
> Although kptr_restrict is set to 0 and the kernel is booted with
> no_hash_pointers parameter, the content of /proc/vmallocinfo is
> lacking the real addresses.
>
> / # cat /proc/vmallocinfo
> 0x(ptrval)-0x(ptrval) 8192 load_module+0xc0c/0x2c0c pages=1 vmalloc
> 0x(ptrval)-0x(ptrval) 12288 start_kernel+0x4e0/0x690 pages=2 vmalloc
> 0x(ptrval)-0x(ptrval) 12288 start_kernel+0x4e0/0x690 pages=2 vmalloc
> 0x(ptrval)-0x(ptrval) 8192 _mpic_map_mmio.constprop.0+0x20/0x44 phys=0x80041000 ioremap
> 0x(ptrval)-0x(ptrval) 12288 _mpic_map_mmio.constprop.0+0x20/0x44 phys=0x80041000 ioremap
> ...
>
> According to the documentation for /proc/sys/kernel/, %pK is
> equivalent to %p when kptr_restrict is set to 0.
Good catch!
BTW: The behavior is strange also when kptr_restrict == 1. It allways
prints non-hashed pointers for user space adresses. It means that
it is less restrictive than kptr_restrict == 0 by default when
no_hash_pointers == 0. It is probably not a big deal but...
> ---
> lib/vsprintf.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 3b8129dd374c..9c60d6e1a0d6 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -857,6 +861,8 @@ char *restricted_pointer(char *buf, char *end, const void *ptr,
> switch (kptr_restrict) {
> case 0:
> /* Handle as %p, hash and do _not_ leak addresses. */
> + if (unlikely(no_hash_pointers))
> + break;
> return ptr_to_id(buf, end, ptr, spec);
This is a twisted duplication of the following code from pointer():
static noinline_for_stack
char *pointer(const char *fmt, char *buf, char *end, void *ptr,
struct printf_spec spec)
{
[...]
/*
* default is to _not_ leak addresses, so hash before printing,
* unless no_hash_pointers is specified on the command line.
*/
if (unlikely(no_hash_pointers))
return pointer_string(buf, end, ptr, spec);
else
return ptr_to_id(buf, end, ptr, spec);
}
Instead, I would create:
/*
* default is to _not_ leak addresses, so hash before printing,
* unless no_hash_pointers is specified on the command line.
*/
static noinline_for_stack
char *default_pointer(const char *fmt, char *buf, char *end, void *ptr,
struct printf_spec spec)
{
if (unlikely(no_hash_pointers))
return pointer_string(buf, end, ptr, spec);
return ptr_to_id(buf, end, ptr, spec);
}
and use it in both hash_pointer() and pointer().
And I would use is also for kptr_restrict == 1. But it probably
should be done in a separate patch and should be acked by Kees.
> case 1: {
> const struct cred *cred;
Best Regards,
Petr
