MIPS: r4k,octeon,r2300: stack protector: change canary per task

For non-SMP, uses the new random canary value that is stored in the
task struct whenever a new task is forked.  Based on ARM version in
df0698be14c6683606d5df2d83e3ae40f85ed0d9 and subject to the same
limitations: the variable GCC expects, __stack_chk_guard, is global,
so this will not work on SMP.

Quoting Nicolas Pitre <nico@fluxnic.net>: "One way to overcome this
GCC limitation would be to locate the __stack_chk_guard variable into
a memory page of its own for each CPU, and then use TLB locking to
have each CPU see its own page at the same virtual address for each of
them."

Signed-off-by: Gregory Fong <gregory.0xf0@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5488/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

4 files changed, 23 insertions, 0 deletions

diff --git a/arch/mips/kernel/asm-offsets.c b/arch/mips/kernel/asm-offsets.c
index 0845091ba480..0c2e853c3db4 100644
--- a/arch/mips/kernel/asm-offsets.c
+++ b/arch/mips/kernel/asm-offsets.c
@@ -82,6 +82,9 @@ void output_task_defines(void)
         OFFSET(TASK_FLAGS, task_struct, flags);
         OFFSET(TASK_MM, task_struct, mm);
         OFFSET(TASK_PID, task_struct, pid);
+#if defined(CONFIG_CC_STACKPROTECTOR)
+        OFFSET(TASK_STACK_CANARY, task_struct, stack_canary);
+#endif
         DEFINE(TASK_STRUCT_SIZE, sizeof(struct task_struct));
         BLANK();
 }
diff --git a/arch/mips/kernel/octeon_switch.S b/arch/mips/kernel/octeon_switch.S
index 22e2aa1e8d37..4204d76af854 100644
--- a/arch/mips/kernel/octeon_switch.S
+++ b/arch/mips/kernel/octeon_switch.S
@@ -71,6 +71,13 @@
         mtc0    t0, $11,7       /* CvmMemCtl */
 #endif
 3:
+
+#if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
+        PTR_L   t8, __stack_chk_guard
+        LONG_L  t9, TASK_STACK_CANARY(a1)
+        LONG_S  t9, 0(t8)
+#endif
+
         /*
          * The order of restoring the registers takes care of the race
          * updating $28, $29 and kernelsp without disabling ints.
diff --git a/arch/mips/kernel/r2300_switch.S b/arch/mips/kernel/r2300_switch.S
index 5266c6ee2b35..38af83f84c4a 100644
--- a/arch/mips/kernel/r2300_switch.S
+++ b/arch/mips/kernel/r2300_switch.S
@@ -65,6 +65,13 @@ LEAF(resume)
         fpu_save_single a0, t0                  # clobbers t0
 
 1:
+
+#if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
+        PTR_L   t8, __stack_chk_guard
+        LONG_L  t9, TASK_STACK_CANARY(a1)
+        LONG_S  t9, 0(t8)
+#endif
+
         /*
          * The order of restoring the registers takes care of the race
          * updating $28, $29 and kernelsp without disabling ints.
diff --git a/arch/mips/kernel/r4k_switch.S b/arch/mips/kernel/r4k_switch.S
index 5e51219990aa..921238a6bd26 100644
--- a/arch/mips/kernel/r4k_switch.S
+++ b/arch/mips/kernel/r4k_switch.S
@@ -68,6 +68,12 @@
                                                 # clobbers t1
 1:
 
+#if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
+        PTR_L   t8, __stack_chk_guard
+        LONG_L  t9, TASK_STACK_CANARY(a1)
+        LONG_S  t9, 0(t8)
+#endif
+
         /*
          * The order of restoring the registers takes care of the race
          * updating $28, $29 and kernelsp without disabling ints.