Re: [PATCH 2/2] arm64: make crash CONFIG_KASAN_HW_TAGS aware

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On 4/26/21 7:17 PM, piliu wrote:

Hi Vinayak,

On 3/30/21 9:52 PM, Vinayak Menon wrote:
With CONFIG_KASAN_HW_TAGS enabled kvaddr can be tagged
and this results in readmem, vtop etc. fail like below.
Sorry for the limited knowledge of this field. I have more question during the reviewing.

-1.is this reproducible with SW TAGS?
-2. HW TAGS aims for malloc, while here I see the handling LR, PC.
It seems that they are more related to "Pointer Authentication"

Thanks,
Pingfan

"
please wait... (gathering kmem slab cache data)
crash: invalid kernel virtual address: f0ffff878000201c  type: "kmem_cache objsize/object_size"
crash: get_active_set: no tasks found?
please wait... (gathering task table data)
crash: invalid kernel virtual address: f1ffff87f51e3530  type: "xa_node shift"
"

Make the mask introduced for pointer authentication generic
and use it in vtop and kvaddr validation.

Signed-off-by: Vinayak Menon <vinayakm.list@xxxxxxxxx>
---
  arm64.c | 50 +++++++++++++++++++++++++++++++-------------------
  defs.h  |  2 +-
  2 files changed, 32 insertions(+), 20 deletions(-)

diff --git a/arm64.c b/arm64.c
index 5b59972..bb41cbb 100644
--- a/arm64.c
+++ b/arm64.c
@@ -85,7 +85,8 @@ static int arm64_get_kvaddr_ranges(struct vaddr_range *);
  static void arm64_get_crash_notes(void);
  static void arm64_calc_VA_BITS(void);
  static int arm64_is_uvaddr(ulong, struct task_context *);
-static void arm64_calc_KERNELPACMASK(void);
+static int arm64_is_kvaddr(ulong);
+static void arm64_calc_KERNELTAGMASK(void);
  /*
@@ -215,7 +216,7 @@ arm64_init(int when)
          machdep->pagemask = ~((ulonglong)machdep->pageoffset);
          arm64_calc_VA_BITS();
-        arm64_calc_KERNELPACMASK();
+        arm64_calc_KERNELTAGMASK();
          ms = machdep->machspec;
          if (ms->VA_BITS_ACTUAL) {
              ms->page_offset = ARM64_PAGE_OFFSET_ACTUAL;
@@ -228,7 +229,7 @@ arm64_init(int when)
              machdep->kvbase = ARM64_VA_START;
              ms->userspace_top = ARM64_USERSPACE_TOP;
          }
-        machdep->is_kvaddr = generic_is_kvaddr;
+        machdep->is_kvaddr = arm64_is_kvaddr;
          machdep->kvtop = arm64_kvtop;
          if (machdep->flags & NEW_VMEMMAP) {
              struct syment *sp;
@@ -477,7 +478,7 @@ arm64_init(int when)
      case LOG_ONLY:
          machdep->machspec = &arm64_machine_specific;
          arm64_calc_VA_BITS();
-        arm64_calc_KERNELPACMASK();
+        arm64_calc_KERNELTAGMASK();
          arm64_calc_phys_offset();
          machdep->machspec->page_offset = ARM64_PAGE_OFFSET;
          arm64_calc_physvirt_offset();
@@ -608,7 +609,7 @@ arm64_dump_machdep_table(ulong arg)
      fprintf(fp, "          dis_filter: arm64_dis_filter()\n");
      fprintf(fp, "            cmd_mach: arm64_cmd_mach()\n");
      fprintf(fp, "        get_smp_cpus: arm64_get_smp_cpus()\n");
-    fprintf(fp, "           is_kvaddr: generic_is_kvaddr()\n");
+    fprintf(fp, "           is_kvaddr: arm64_is_kvaddr()\n");
      fprintf(fp, "           is_uvaddr: arm64_is_uvaddr()\n");
      fprintf(fp, "     value_to_symbol: generic_machdep_value_to_symbol()\n");
      fprintf(fp, "     init_kernel_pgd: arm64_init_kernel_pgd\n");
@@ -668,9 +669,9 @@ arm64_dump_machdep_table(ulong arg)
          fprintf(fp, "%ld\n", ms->VA_BITS_ACTUAL);
      else
          fprintf(fp, "(unused)\n");
-    fprintf(fp, "CONFIG_ARM64_KERNELPACMASK: ");
-    if (ms->CONFIG_ARM64_KERNELPACMASK)
-        fprintf(fp, "%lx\n", ms->CONFIG_ARM64_KERNELPACMASK);
+    fprintf(fp, "CONFIG_ARM64_KERNELTAGMASK: ");
+    if (ms->CONFIG_ARM64_KERNELTAGMASK)
+        fprintf(fp, "%lx\n", ms->CONFIG_ARM64_KERNELTAGMASK);
      else
          fprintf(fp, "(unused)\n");
      fprintf(fp, "         userspace_top: %016lx\n", ms->userspace_top);
@@ -1208,6 +1209,9 @@ arm64_kvtop(struct task_context *tc, ulong kvaddr, physaddr_t *paddr, int verbos
      if (!IS_KVADDR(kvaddr))
          return FALSE;
+    if (kvaddr & (1UL << 63))
+        kvaddr |= machdep->machspec->CONFIG_ARM64_KERNELTAGMASK;
+
      if (!vt->vmalloc_start) {
          *paddr = VTOP(kvaddr);
          return TRUE;
@@ -1828,7 +1832,7 @@ arm64_is_kernel_exception_frame(struct bt_info *bt, ulong stkptr)
      if (INSTACK(regs->sp, bt) && INSTACK(regs->regs[29], bt) &&
          !(regs->pstate & (0xffffffff00000000ULL | PSR_MODE32_BIT)) &&
          is_kernel_text(regs->pc) &&
-        is_kernel_text(regs->regs[30] | ms->CONFIG_ARM64_KERNELPACMASK)) { +        is_kernel_text(regs->regs[30] | ms->CONFIG_ARM64_KERNELTAGMASK)) {
          switch (regs->pstate & PSR_MODE_MASK)
          {
          case PSR_MODE_EL1t:
@@ -2198,8 +2202,8 @@ arm64_unwind_frame(struct bt_info *bt, struct arm64_stackframe *frame)
      frame->sp = fp + 0x10;
      frame->fp = GET_STACK_ULONG(fp);
      frame->pc = GET_STACK_ULONG(fp + 8);
-    if (is_kernel_text(frame->pc | ms->CONFIG_ARM64_KERNELPACMASK))
-        frame->pc |= ms->CONFIG_ARM64_KERNELPACMASK;
+    if (is_kernel_text(frame->pc | ms->CONFIG_ARM64_KERNELTAGMASK))
+        frame->pc |= ms->CONFIG_ARM64_KERNELTAGMASK;
      if ((frame->fp == 0) && (frame->pc == 0))
          return FALSE;
@@ -2869,8 +2873,8 @@ arm64_print_text_symbols(struct bt_info *bt, struct arm64_stackframe *frame, FIL       for (i = (start - bt->stackbase)/sizeof(ulong); i < LONGS_PER_STACK; i++) {
          up = (ulong *)(&bt->stackbuf[i*sizeof(ulong)]);
          val = *up;
-        if (is_kernel_text(val | ms->CONFIG_ARM64_KERNELPACMASK)) {
-            val |= ms->CONFIG_ARM64_KERNELPACMASK;
+        if (is_kernel_text(val | ms->CONFIG_ARM64_KERNELTAGMASK)) {
+            val |= ms->CONFIG_ARM64_KERNELTAGMASK;
              name = closest_symbol(val);
              fprintf(ofp, "  %s[%s] %s at %lx",
                  bt->flags & BT_ERROR_MASK ?
@@ -3205,8 +3209,8 @@ arm64_print_exception_frame(struct bt_info *bt, ulong pt_regs, int mode, FILE *o
          rows = 4;
      } else {
          LR = regs->regs[30];
-        if (is_kernel_text (LR | ms->CONFIG_ARM64_KERNELPACMASK))
-            LR |= ms->CONFIG_ARM64_KERNELPACMASK;
+        if (is_kernel_text (LR | ms->CONFIG_ARM64_KERNELTAGMASK))
+            LR |= ms->CONFIG_ARM64_KERNELTAGMASK;
          SP = regs->sp;
          top_reg = 29;
          is_64_bit = TRUE;
@@ -4102,6 +4106,14 @@ arm64_calc_virtual_memory_ranges(void)
  }
  static int
+arm64_is_kvaddr(ulong addr)
+{
+    if (addr & (1UL << 63))
+        addr |= machdep->machspec->CONFIG_ARM64_KERNELTAGMASK;
+    return generic_is_kvaddr(addr);
+}
+
+static int
  arm64_is_uvaddr(ulong addr, struct task_context *tc)
  {
          return (addr < machdep->machspec->userspace_top);
@@ -4129,21 +4141,21 @@ arm64_swp_offset(ulong pte)
      return pte;
  }
-static void arm64_calc_KERNELPACMASK(void)
+static void arm64_calc_KERNELTAGMASK(void)
  {
      ulong value = 0;
      char *string;
-    if ((string = pc->read_vmcoreinfo("NUMBER(KERNELPACMASK)"))) {
+    if ((string = pc->read_vmcoreinfo("NUMBER(KERNELTAGMASK)"))) {

I git grep 5.12 kernel, but did not find this. Do you plan to do it in kernel firstly?

Thanks,
Pingfan
          value = htol(string, QUIET, NULL);
          free(string);
      } else if (machdep->machspec->tag_mask) {
          value = machdep->machspec->tag_mask;
      }
-    machdep->machspec->CONFIG_ARM64_KERNELPACMASK = value;
+    machdep->machspec->CONFIG_ARM64_KERNELTAGMASK = value;
      if (CRASHDEBUG(1))
-        fprintf(fp, "CONFIG_ARM64_KERNELPACMASK: %lx\n", value);
+        fprintf(fp, "CONFIG_ARM64_KERNELTAGMASK: %lx\n", value);
  }
  #endif  /* ARM64 */
diff --git a/defs.h b/defs.h
index d406f5f..770c335 100644
--- a/defs.h
+++ b/defs.h
@@ -3329,7 +3329,7 @@ struct machine_specific {
      ulong VA_BITS_ACTUAL;
      ulong CONFIG_ARM64_VA_BITS;
      ulong VA_START;
-    ulong CONFIG_ARM64_KERNELPACMASK;
+    ulong CONFIG_ARM64_KERNELTAGMASK;
      ulong physvirt_offset;
      ulong tag_mask;
  };

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