If we use crash tool to parse ramdump(Qcom phone device) rather than vmcore.

Start command should be like: crash vmlinux --kaslr=xxx DDRCS0_0.BIN@0x0000000080000000,... --machdep vabits_actual=39

Then We will see bt command show misleading backtrace information as:


crash> bt 16930

PID: 16930    TASK: ffffff89b3eada00  CPU: 2    COMMAND: "Firebase Backgr"

 #0 [ffffffc034c437f0] __switch_to at ffffffe0036832d4

 #1 [ffffffc034c43850] __kvm_nvhe_$d.2314 at 6be732e004cf05a0

 #2 [ffffffc034c438b0] __kvm_nvhe_$d.2314 at 86c54c6004ceff80

 #3 [ffffffc034c43950] __kvm_nvhe_$d.2314 at 55d6f96003a7b120

 #4 [ffffffc034c439f0] __kvm_nvhe_$d.2314 at 9ccec46003a80a64

 #5 [ffffffc034c43ac0] __kvm_nvhe_$d.2314 at 8cf41e6003a945c4

 #6 [ffffffc034c43b10] __kvm_nvhe_$d.2314 at a8f181e00372c818

 #7 [ffffffc034c43b40] __kvm_nvhe_$d.2314 at 6dedde600372c0d0

 #8 [ffffffc034c43b90] __kvm_nvhe_$d.2314 at 62cc07e00373d0ac

 #9 [ffffffc034c43c00] __kvm_nvhe_$d.2314 at 72fb1de00373bedc

...

     PC: 00000073f5294840   LR: 00000070d8f39ba4   SP: 00000070d4afd5d0

    X29: 00000070d4afd600  X28: b4000071efcda7f0  X27: 00000070d4afe000

    X26: 0000000000000000  X25: 00000070d9616000  X24: 0000000000000000

    X23: 0000000000000000  X22: 0000000000000000  X21: 0000000000000000

    X20: b40000728fd27520  X19: b40000728fd27550  X18: 000000702daba000

    X17: 00000073f5294820  X16: 00000070d940f9d8  X15: 00000000000000bf

    X14: 0000000000000000  X13: 00000070d8ad2fac  X12: b40000718fce5040

    X11: 0000000000000000  X10: 0000000000000070   X9: 0000000000000001

     X8: 0000000000000062   X7: 0000000000000020   X6: 0000000000000000

     X5: 0000000000000000   X4: 0000000000000000   X3: 0000000000000000

     X2: 0000000000000002   X1: 0000000000000080   X0: b40000728fd27550

    ORIG_X0: b40000728fd27550  SYSCALLNO: ffffffff  PSTATE: 40001000


By checking the raw data below, will see the lr (fp+8) data show the pointer which already been replaced by PAC prefix.


crash> bt -f

PID: 16930    TASK: ffffff89b3eada00  CPU: 2    COMMAND: "Firebase Backgr"

 #0 [ffffffc034c437f0] __switch_to at ffffffe0036832d4

    ffffffc034c437f0: ffffffc034c43850 6be732e004cf05a4

    ffffffc034c43800: ffffffe006186108 a0ed07e004cf09c4

    ffffffc034c43810: ffffff8a1a340000 ffffff8a8d343c00

    ffffffc034c43820: ffffff89b3eada00 ffffff8b780db540

    ffffffc034c43830: ffffff89b3eada00 0000000000000000

    ffffffc034c43840: 0000000000000004 712b828118484a00

 #1 [ffffffc034c43850] __kvm_nvhe_$d.2314 at 6be732e004cf05a0

    ffffffc034c43850: ffffffc034c438b0 86c54c6004ceff84

    ffffffc034c43860: 000000708070f000 ffffffc034c43938

    ffffffc034c43870: ffffff88bd822878 ffffff89b3eada00

...


So we may search the CONFIG_ARM64_PTR_AUTH_KERNEL to double check if pac mechanism has been enabled on this ramdump.


Luckily, lijiang and tao give some valuable suggestion:

As IKCONFIG may not available in most distributions.

So we could check if the "struct ptrauth_keys_kernel" has already been embeded into arm's thread structure.


  struct thread_struct {

   struct cpu_context cpu_context; /* cpu context */

  ...

  #ifdef CONFIG_ARM64_PTR_AUTH

   struct ptrauth_keys_user keys_user;

  #ifdef CONFIG_ARM64_PTR_AUTH_KERNEL

   struct ptrauth_keys_kernel keys_kernel;

  #endif

  ...

  };


PAC feature should be enabled when "struct ptrauth_keys_kernel" exist, and we can use vabits to figure out pac bitmask.


The fix backtrace is shown below:

crash> bt 16930

PID: 16930    TASK: ffffff89b3eada00  CPU: 2    COMMAND: "Firebase Backgr"

 #0 [ffffffc034c437f0] __switch_to at ffffffe0036832d4

 #1 [ffffffc034c43850] __schedule at ffffffe004cf05a0

 #2 [ffffffc034c438b0] preempt_schedule_common at ffffffe004ceff80

 #3 [ffffffc034c43950] unmap_page_range at ffffffe003a7b120

 #4 [ffffffc034c439f0] unmap_vmas at ffffffe003a80a64

 #5 [ffffffc034c43ac0] exit_mmap at ffffffe003a945c4

 #6 [ffffffc034c43b10] __mmput at ffffffe00372c818

 #7 [ffffffc034c43b40] mmput at ffffffe00372c0d0

 #8 [ffffffc034c43b90] exit_mm at ffffffe00373d0ac

 #9 [ffffffc034c43c00] do_exit at ffffffe00373bedc

     PC: 00000073f5294840   LR: 00000070d8f39ba4   SP: 00000070d4afd5d0

    X29: 00000070d4afd600  X28: b4000071efcda7f0  X27: 00000070d4afe000

    X26: 0000000000000000  X25: 00000070d9616000  X24: 0000000000000000

    X23: 0000000000000000  X22: 0000000000000000  X21: 0000000000000000

    X20: b40000728fd27520  X19: b40000728fd27550  X18: 000000702daba000

    X17: 00000073f5294820  X16: 00000070d940f9d8  X15: 00000000000000bf

    X14: 0000000000000000  X13: 00000070d8ad2fac  X12: b40000718fce5040

    X11: 0000000000000000  X10: 0000000000000070   X9: 0000000000000001

     X8: 0000000000000062   X7: 0000000000000020   X6: 0000000000000000

     X5: 0000000000000000   X4: 0000000000000000   X3: 0000000000000000

     X2: 0000000000000002   X1: 0000000000000080   X0: b40000728fd27550

    ORIG_X0: b40000728fd27550  SYSCALLNO: ffffffff  PSTATE: 40001000


Here is gki's PAC related original commit for reference:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Author: Amit Daniel Kachhap <amit.kachhap@arm.com>

Date:   Fri Mar 13 14:34:58 2020 +0530


    arm64: mask PAC bits of __builtin_return_address


    Functions like vmap() record how much memory has been allocated by their

    callers, and callers are identified using __builtin_return_address(). Once

    the kernel is using pointer-auth the return address will be signed. This

    means it will not match any kernel symbol, and will vary between threads

    even for the same caller.


    The output of /proc/vmallocinfo in this case may look like,

    0x(____ptrval____)-0x(____ptrval____)   20480 0x86e28000100e7c60 pages=4 vmalloc N0=4

    0x(____ptrval____)-0x(____ptrval____)   20480 0x86e28000100e7c60 pages=4 vmalloc N0=4

    0x(____ptrval____)-0x(____ptrval____)   20480 0xc5c78000100e7c60 pages=4 vmalloc N0=4


    The above three 64bit values should be the same symbol name and not

    different LR values.


    Use the pre-processor to add logic to clear the PAC to

    __builtin_return_address() callers. This patch adds a new file

    asm/compiler.h and is transitively included via include/compiler_types.h on

    the compiler command line so it is guaranteed to be loaded and the users of

    this macro will not find a wrong version.


    Helper macros ptrauth_kernel_pac_mask/ptrauth_clear_pac are created for

    this purpose and added in this file. Existing macro ptrauth_user_pac_mask

    moved from asm/pointer_auth.h.


    Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com>

    Reviewed-by: James Morse <james.morse@arm.com>

    Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>


diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig

index 87e2cbb76930..115ceea0293e 100644

--- a/arch/arm64/Kconfig

+++ b/arch/arm64/Kconfig

@@ -118,6 +118,7 @@ config ARM64

        select HAVE_ALIGNED_STRUCT_PAGE if SLUB

        select HAVE_ARCH_AUDITSYSCALL

        select HAVE_ARCH_BITREVERSE

+       select HAVE_ARCH_COMPILER_H

        select HAVE_ARCH_HUGE_VMAP

        select HAVE_ARCH_JUMP_LABEL

        select HAVE_ARCH_JUMP_LABEL_RELATIVE

diff --git a/arch/arm64/include/asm/compiler.h b/arch/arm64/include/asm/compiler.h

new file mode 100644

index 000000000000..eece20d2c55f

--- /dev/null

+++ b/arch/arm64/include/asm/compiler.h

@@ -0,0 +1,24 @@

+/* SPDX-License-Identifier: GPL-2.0 */

+#ifndef __ASM_COMPILER_H

+#define __ASM_COMPILER_H

+

+#if defined(CONFIG_ARM64_PTR_AUTH)

+

+/*

+ * The EL0/EL1 pointer bits used by a pointer authentication code.

+ * This is dependent on TBI0/TBI1 being enabled, or bits 63:56 would also apply.

+ */

+#define ptrauth_user_pac_mask()                GENMASK_ULL(54, vabits_actual)

+#define ptrauth_kernel_pac_mask()      GENMASK_ULL(63, vabits_actual)

+

+/* Valid for EL0 TTBR0 and EL1 TTBR1 instruction pointers */

+#define ptrauth_clear_pac(ptr)                                         \

+       ((ptr & BIT_ULL(55)) ? (ptr | ptrauth_kernel_pac_mask()) :      \

+                              (ptr & ~ptrauth_user_pac_mask()))

+

+#define __builtin_return_address(val)                                  \

+       (void *)(ptrauth_clear_pac((unsigned long)__builtin_return_address(val)))

+

+#endif /* CONFIG_ARM64_PTR_AUTH */

+

+#endif /* __ASM_COMPILER_H */

diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h

index 833d3f948de0..70c47156e54b 100644

--- a/arch/arm64/include/asm/pointer_auth.h

+++ b/arch/arm64/include/asm/pointer_auth.h

@@ -68,16 +68,9 @@ static __always_inline void ptrauth_keys_switch_kernel(struct ptrauth_keys_kerne


 extern int ptrauth_prctl_reset_keys(struct task_struct *tsk, unsigned long arg);


-/*

- * The EL0 pointer bits used by a pointer authentication code.

- * This is dependent on TBI0 being enabled, or bits 63:56 would also apply.

- */

-#define ptrauth_user_pac_mask()        GENMASK(54, vabits_actual)

-

-/* Only valid for EL0 TTBR0 instruction pointers */

 static inline unsigned long ptrauth_strip_insn_pac(unsigned long ptr)

 {

-       return ptr & ~ptrauth_user_pac_mask();

+       return ptrauth_clear_pac(ptr);

 }


 #define ptrauth_thread_init_user(tsk)

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Signed-off-by: bevis_chen <bevis_chen@asus.com>

---

 arm64.c | 27 +++++++++++++++++++++++++++

 1 file changed, 27 insertions(+)


diff --git a/arm64.c b/arm64.c

index b3040d7..50dd458 100644

--- a/arm64.c

+++ b/arm64.c

@@ -92,6 +92,7 @@ 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 void arm64_recalc_KERNELPACMASK(void);

 static int arm64_get_vmcoreinfo(unsigned long *vaddr, const char *label, int base);


 struct kernel_range {

@@ -581,6 +582,17 @@ arm64_init(int when)

                if (!machdep->hz)

                        machdep->hz = 100;


+               /*

+               * In the case of using ramdump rather than vmcore,

+               * will fail to parse out KERNELPAC.

+               * So we check if the "sturct ptrauth_keys_kernel" exits

+               * as a basis for whether PAC feature is enabled or not.

+               * If yes, then we use vabits to figure out pac bitmask.

+               */

+               if(!machdep->machspec->CONFIG_ARM64_KERNELPACMASK)

+                       arm64_recalc_KERNELPACMASK();

+

+

                arm64_irq_stack_init();

                arm64_overflow_stack_init();

                arm64_stackframe_init();

@@ -4921,6 +4933,21 @@ static void arm64_calc_KERNELPACMASK(void)

        }

 }


+

+#define GENMASK_UL(h, l) \

+    (((~0UL) << (l)) & (~0UL >> (BITS_PER_LONG - 1 - (h))))

+

+static void arm64_recalc_KERNELPACMASK(void){

+       /* arm64: check if pac already enabled yet from related structure.*/

+       if (STRUCT_EXISTS("ptrauth_keys_kernel") && machdep->machspec->VA_BITS_ACTUAL){

+               machdep->machspec->CONFIG_ARM64_KERNELPACMASK =

+                       GENMASK_UL(63, machdep->machspec->VA_BITS_ACTUAL);

+               if (CRASHDEBUG(1))

+                       fprintf(fp, "CONFIG_ARM64_KERNELPACMASK: %lx\n",

+                               machdep->machspec->CONFIG_ARM64_KERNELPACMASK);

+       }

+}

+

 #endif  /* ARM64 */



--

2.27.0