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  1. 26 May, 2008 2 commits
    • Ingo Molnar's avatar
      x86: fix stackprotector canary updates during context switches · e0032087
      Ingo Molnar authored 
      fix a bug noticed and fixed by pageexec@freemail.hu.

if built with -fstack-protector-all then we'll have canary checks built
into the __switch_to() function. That does not work well with the
canary-switching code there: while we already use the %rsp of the
new task, we still call __switch_to() whith the previous task's canary
value in the PDA, hence the __switch_to() ssp prologue instructions
will store the previous canary. Then we update the PDA and upon return
from __switch_to() the canary check triggers and we panic.

so update the canary after we have called __switch_to(), where we are
at the same stackframe level as the last stackframe of the next
(and now freshly current) task.

Note: this means that we call __switch_to() [and its sub-functions]
still with the old canary, but that is not a problem, both the previous
and the next task has a high-quality canary. The only (mostly academic)
disadvantage is that the canary of one task may leak onto the stack of
another task, increasing the risk of information leaks, were an attacker
able to read the stack of specific tasks (but not that of others).

To solve this we'll have to reorganize the way we switch tasks, and move
the PDA setting into the switch_to() assembly code. That will happen in
another patch.
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      e0032087
    • Ingo Molnar's avatar
      x86: stackprotector & PARAVIRT fix · 4c7f8900
      Ingo Molnar authored 
      on paravirt enabled 64-bit kernels the paravirt ops do function
calls themselves - which is bad with the stackprotector - for
example pda_init() loads 0 into %gs and then does MSR_GS_BASE
write (which modifies gs.base) - but that MSR write is a function
call on paravirt, which with stackprotector tries to read the
stack canary from the PDA ... crashing the bootup.

the solution was suggested by Arjan van de Ven: to exclude paravirt.c
from stackprotector, too many lowlevel functionality is in it. It's
not like we'll have paravirt functions with character arrays on
their stack anyway...
Signed-off-by: default avatarArjan van de Ven <arjan@linux.intel.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      4c7f8900
  3. 25 May, 2008 16 commits
  5. 24 May, 2008 22 commits
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