x86/pti: Switch to kernel CR3 at early in entry_SYSCALL_compat()
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>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1801031949200.1957@nanos
This commit is contained in:
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@ -190,8 +190,13 @@ ENTRY(entry_SYSCALL_compat)
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/* Interrupts are off on entry. */
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swapgs
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/* Stash user ESP and switch to the kernel stack. */
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/* Stash user ESP */
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movl %esp, %r8d
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/* Use %rsp as scratch reg. User ESP is stashed in r8 */
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SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp
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/* Switch to the kernel stack */
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movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
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/* Construct struct pt_regs on stack */
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@ -219,12 +224,6 @@ GLOBAL(entry_SYSCALL_compat_after_hwframe)
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pushq $0 /* pt_regs->r14 = 0 */
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pushq $0 /* pt_regs->r15 = 0 */
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/*
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* We just saved %rdi so it is safe to clobber. It is not
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* preserved during the C calls inside TRACE_IRQS_OFF anyway.
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*/
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SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi
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/*
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* User mode is traced as though IRQs are on, and SYSENTER
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* turned them off.
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