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x86: fix trampoline stack clobber 

We need to lock interrupts before setting the thread's
stack pointer to the trampoline stack. Otherwise, we
could unexpectedly take an interrupt on this stack
instead of the thread stack as intended.

The specific problem happens at the end of the interrupt,
when we switch back to the thread stack and call swap.
Doing this on a per-cpu trampoline stack instead of the
thread stack causes data corruption.

Fixes: #24869

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
This commit is contained in:
Andrew Boie 2020-04-30 16:46:29 -07:00 committed by Andrew Boie
parent 7ede80be46
commit dac61f450d
1 changed files with 6 additions and 6 deletions
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12
arch/x86/core/ia32/userspace.S
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@ -110,14 +110,14 @@ SECTION_FUNC(TEXT, z_x86_trampoline_to_user_always)
/* Stash EDI, need a free register */
pushl %edi
/* Store old stack pointer and switch to trampoline stack */
movl %esp, %edi
movl $z_trampoline_stack_end, %esp
/* Lock IRQs until we get out, we don't want anyone else using the
* trampoline stack
/* Store old stack pointer and switch to trampoline stack.
* Lock IRQs before changing stack pointer to the trampoline stack,
* we don't want any interrupts also using the trampoline stack
* during this time.
*/
movl %esp, %edi
cli
movl $z_trampoline_stack_end, %esp
/* Copy context */
pushl 20(%edi) /* SS */