Messages in this thread | | | Subject | Re: [PATCH v2] ppc64/kprobe: Fix oops when kprobed on 'stdu' instruction | From | Ravi Bangoria <> | Date | Tue, 11 Apr 2017 16:22:18 +0530 |
| |
Thanks Balbir for the review,
On Tuesday 11 April 2017 02:25 PM, Balbir Singh wrote: > On Tue, 2017-04-11 at 10:38 +0530, Ravi Bangoria wrote: >> If we set a kprobe on a 'stdu' instruction on powerpc64, we see a kernel >> OOPS: >> >> [ 1275.165932] Bad kernel stack pointer cd93c840 at c000000000009868 >> [ 1275.166378] Oops: Bad kernel stack pointer, sig: 6 [#1] >> ... >> GPR00: c000001fcd93cb30 00000000cd93c840 c0000000015c5e00 00000000cd93c840 >> ... >> [ 1275.178305] NIP [c000000000009868] resume_kernel+0x2c/0x58 >> [ 1275.178594] LR [c000000000006208] program_check_common+0x108/0x180 >> >> Basically, on 64 bit system, when user probes on 'stdu' instruction, >> kernel does not emulate actual store in emulate_step itself because it >> may corrupt exception frame. So kernel does actual store operation in >> exception return code i.e. resume_kernel(). >> >> resume_kernel() loads the saved stack pointer from memory using lwz, >> effectively loading a corrupt (32bit) address, causing the kernel crash. >> >> Fix this by loading the 64bit value instead. >> >> Fixes: be96f63375a1 ("powerpc: Split out instruction analysis part of emulate_step()") >> Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com> >> Reviewed-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> >> --- > The patch looks correct to me from the description and code. I have not > validated that the write to GPR1(r1) via store of r8 to 0(r5) is indeed correct. > I would assume r8 should contain regs->gpr[r1] with the updated ea that > is written down to the GPR1(r1) which will be what we restore when we return > from the exception.
emulate_step() updates regs->gpr[r1] with the new value. So, regs->gpr[r1] and GPR(r1) both are same at resume_kernel.
At resume_kernel, r1 points to the exception frame. Address of frame preceding exception frame gets loaded in r8 with:
addi r8,r1,INT_FRAME_SIZE
Let me know if you need more details.
Ravi
| |