On 2020/12/22 1:12, Segher Boessenkool wrote:
On Mon, Dec 21, 2020 at 04:42:23PM +0000, David Laight wrote:
From: Segher Boessenkool
Sent: 21 December 2020 16:32
On Mon, Dec 21, 2020 at 04:17:21PM +0100, Christophe Leroy wrote:
Le 21/12/2020 à 04:27, Xiaoming Ni a écrit :
Since the commit 2b0e86cc5de6 ("powerpc/fsl_booke/32: implement KASLR
infrastructure"), the powerpc system is ready to support KASLR.
To reduces the risk of invalidating address randomization, don't print the
EIP/LR hex values in dump_stack() and show_regs().
I think your change is not enough to hide EIP address, see below a dump
with you patch, you get "Faulting instruction address: 0xc03a0c14"
As far as I can see the patch does nothing to the GPR printout. Often
GPRs contain code addresses. As one example, the LR is moved via a GPR
(often GPR0, but not always) for storing on the stack.
So this needs more work.
If the dump_stack() is from an oops you need the real EIP value
on order to stand any chance of making headway.
Or at least the function name + offset, yes.
When the system is healthy, only symbols and offsets are printed,
Output address and symbol + offset when the system is dying
Does this meet both debugging and security requirements?
For example:
+static void __show_regs_ip_lr(const char *flag, unsigned long addr)
+{
+ if (system_going_down()) { /* panic oops reboot */
+ pr_cont("%s["REG"] %pS", flag, addr, (void *)addr);
+ } else {
+ pr_cont("%s%pS", flag, (void *)addr);
+ }
+}
+
static void __show_regs(struct pt_regs *regs)
{
int i, trap;
- printk("NIP: "REG" LR: "REG" CTR: "REG"\n",
- regs->nip, regs->link, regs->ctr);
+ __show_regs_ip_lr("NIP: ", regs->nip);
+ __show_regs_ip_lr(" LR: ", regs->link);
+ pr_cont(" CTR: "REG"\n", regs->ctr);
printk("REGS: %px TRAP: %04lx %s (%s)\n",
regs, regs->trap, print_tainted(), init_utsname()->release);
printk("MSR: "REG" ", regs->msr);
Otherwise you might just as well just print 'borked - tough luck'.
Yes. ASLR is a house of cards. But that isn't constructive wrt this
patch :-)
Segher
.
Thanks
Xiaoming Ni
