Commit a8c715b4 authored May 13, 2019 by Eugeniy Paltsev Committed by Vineet Gupta May 20, 2019

ARC: mm: SIGSEGV userspace trying to access kernel virtual memory



As of today if userspace process tries to access a kernel virtual addres
(0x7000_0000 to 0x7ffff_ffff) such that a legit kernel mapping already
exists, that process hangs instead of being killed with SIGSEGV

Fix that by ensuring that do_page_fault() handles kenrel vaddr only if
in kernel mode.

And given this, we can also simplify the code a bit. Now a vmalloc fault
implies kernel mode so its failure (for some reason) can reuse the
@no_context label and we can remove @bad_area_nosemaphore.

Reproduce user test for original problem:

------------------------>8-----------------
 #include <stdlib.h>
 #include <stdint.h>

 int main(int argc, char *argv[])
 {
 	volatile uint32_t temp;

 	temp = *(uint32_t *)(0x70000000);
 }
------------------------>8-----------------

Cc: <stable@vger.kernel.org>
Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

parent 89c92142

arch/arc/mm/fault.c

+3 −6

Original line number	Diff line number	Diff line
		@@ -66,7 +66,7 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
		struct vm_area_struct *vma = NULL;
		struct task_struct *tsk = current;
		struct mm_struct *mm = tsk->mm;
		int si_code = 0;
		int si_code = SEGV_MAPERR;
		int ret;
		vm_fault_t fault;
		int write = regs->ecr_cause & ECR_C_PROTV_STORE; /* ST/EX */
		@@ -81,16 +81,14 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
		* only copy the information from the master page table,
		* nothing more.
		*/
		if (address >= VMALLOC_START) {
		if (address >= VMALLOC_START && !user_mode(regs)) {
		ret = handle_kernel_vaddr_fault(address);
		if (unlikely(ret))
		goto bad_area_nosemaphore;
		goto no_context;
		else
		return;
		}

		si_code = SEGV_MAPERR;

		/*
		* If we're in an interrupt or have no user
		* context, we must not take the fault..
		@@ -198,7 +196,6 @@ good_area:
		bad_area:
		up_read(&mm->mmap_sem);

		bad_area_nosemaphore:
		/* User mode accesses just cause a SIGSEGV */
		if (user_mode(regs)) {
		tsk->thread.fault_address = address;

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