ARM: unwind: support unwinding across multiple stacks

Implement support in the unwinder for dealing with multiple stacks.
This will be needed once we add support for IRQ stacks, or for the
overflow stack used by the vmap'ed stacks code.

This involves tracking the unwind opcodes that either update the virtual
stack pointer from another virtual register, or perform an explicit
subtract on the virtual stack pointer, and updating the low and high
bounds that we use to sanitize the stack pointer accordingly.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Keith Packard <keithpac@amazon.com>
Tested-by: Marc Zyngier <maz@kernel.org>
Tested-by: Vladimir Murzin <vladimir.murzin@arm.com> # ARMv7M

diff --git a/arch/arm/kernel/unwind.c b/arch/arm/kernel/unwind.c
index 59fdf257bf8be78e4ed7a6cfb19f43c1822935ef..9cb9af3fc43398c43b294108e815afe1da7ed18a 100644 (file)
--- a/arch/arm/kernel/unwind.c
+++ b/arch/arm/kernel/unwind.c
@@ -52,6 +52,7 @@ EXPORT_SYMBOL(__aeabi_unwind_cpp_pr2);
 struct unwind_ctrl_block {
        unsigned long vrs[16];          /* virtual register set */
        const unsigned long *insn;      /* pointer to the current instructions word */
+       unsigned long sp_low;           /* lowest value of sp allowed */
        unsigned long sp_high;          /* highest value of sp allowed */
        /*
         * 1 : check for stack overflow for each register pop.
@@ -256,8 +257,12 @@ static int unwind_exec_pop_subset_r4_to_r13(struct unwind_ctrl_block *ctrl,
                mask >>= 1;
                reg++;
        }
-       if (!load_sp)
+       if (!load_sp) {
                ctrl->vrs[SP] = (unsigned long)vsp;
+       } else {
+               ctrl->sp_low = ctrl->vrs[SP];
+               ctrl->sp_high = ALIGN(ctrl->sp_low, THREAD_SIZE);
+       }
 
        return URC_OK;
 }
@@ -313,9 +318,10 @@ static int unwind_exec_insn(struct unwind_ctrl_block *ctrl)
 
        if ((insn & 0xc0) == 0x00)
                ctrl->vrs[SP] += ((insn & 0x3f) << 2) + 4;
-       else if ((insn & 0xc0) == 0x40)
+       else if ((insn & 0xc0) == 0x40) {
                ctrl->vrs[SP] -= ((insn & 0x3f) << 2) + 4;
-       else if ((insn & 0xf0) == 0x80) {
+               ctrl->sp_low = ctrl->vrs[SP];
+       } else if ((insn & 0xf0) == 0x80) {
                unsigned long mask;
 
                insn = (insn << 8) | unwind_get_byte(ctrl);
@@ -330,9 +336,11 @@ static int unwind_exec_insn(struct unwind_ctrl_block *ctrl)
                if (ret)
                        goto error;
        } else if ((insn & 0xf0) == 0x90 &&
-                  (insn & 0x0d) != 0x0d)
+                  (insn & 0x0d) != 0x0d) {
                ctrl->vrs[SP] = ctrl->vrs[insn & 0x0f];
-       else if ((insn & 0xf0) == 0xa0) {
+               ctrl->sp_low = ctrl->vrs[SP];
+               ctrl->sp_high = ALIGN(ctrl->sp_low, THREAD_SIZE);
+       } else if ((insn & 0xf0) == 0xa0) {
                ret = unwind_exec_pop_r4_to_rN(ctrl, insn);
                if (ret)
                        goto error;
@@ -375,13 +383,12 @@ error:
  */
 int unwind_frame(struct stackframe *frame)
 {
-       unsigned long low;
        const struct unwind_idx *idx;
        struct unwind_ctrl_block ctrl;
 
        /* store the highest address on the stack to avoid crossing it*/
-       low = frame->sp;
-       ctrl.sp_high = ALIGN(low, THREAD_SIZE);
+       ctrl.sp_low = frame->sp;
+       ctrl.sp_high = ALIGN(ctrl.sp_low, THREAD_SIZE);
 
        pr_debug("%s(pc = %08lx lr = %08lx sp = %08lx)\n", __func__,
                 frame->pc, frame->lr, frame->sp);
@@ -437,7 +444,7 @@ int unwind_frame(struct stackframe *frame)
                urc = unwind_exec_insn(&ctrl);
                if (urc < 0)
                        return urc;
-               if (ctrl.vrs[SP] < low || ctrl.vrs[SP] >= ctrl.sp_high)
+               if (ctrl.vrs[SP] < ctrl.sp_low || ctrl.vrs[SP] > ctrl.sp_high)
                        return -URC_FAILURE;
        }