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Subject[PATCH 5.1 24/70] ARC: mm: SIGSEGV userspace trying to access kernel virtual memory
Date
From: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>

commit a8c715b4dd73c26a81a9cc8dc792aa715d8b4bb2 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arc/mm/fault.c | 9 +++------
1 file changed, 3 insertions(+), 6 deletions(-)

--- a/arch/arc/mm/fault.c
+++ b/arch/arc/mm/fault.c
@@ -66,7 +66,7 @@ void do_page_fault(unsigned long address
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
* 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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