x86/pti: Switch to kernel CR3 at early in entry_SYSCALL_compat()

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commit d7732ba55c upstream.

The preparation for PTI which added CR3 switching to the entry code
misplaced the CR3 switch in entry_SYSCALL_compat().

With PTI enabled the entry code tries to access a per cpu variable after
switching to kernel GS. This fails because that variable is not mapped to
user space. This results in a double fault and in the worst case a kernel
crash.

Move the switch ahead of the access and clobber RSP which has been saved
already.

Fixes: 8a09317b89 ("x86/mm/pti: Prepare the x86/entry assembly code for entry/exit CR3 switching")
Reported-by: Lars Wendler <wendler.lars@web.de>
Reported-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@kernel.org>,
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
Cc: Peter Zijlstra <peterz@infradead.org>,
Cc: Greg KH <gregkh@linuxfoundation.org>, ,
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Cc: Juergen Gross <jgross@suse.com>
Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1801031949200.1957@nanos
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

...

This commit is contained in:

Thomas Gleixner 2018-01-03 19:52:04 +01:00 • committed by Greg Kroah-Hartman

parent 89c96233a9

commit 7930cb29fb

1 changed files with 6 additions and 7 deletions

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arch/x86/entry/entry_64_compat.S

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