Thank you for the patch, Guanyou.
On Tue, Dec 31, 2024 at 7:22 PM <devel-requ...@lists.crash-utility.osci.io>
wrote:
> Date: Thu, 26 Dec 2024 00:08:50 +0800
> From: Guanyou Chen <chenguanyou9...@gmail.com>
> Subject: [Crash-utility] [PATCH] arm64: add pac mask to better support
> gdb stack unwind
> To: Lianbo <liji...@redhat.com>, Tao Liu <l...@redhat.com>,
> devel@lists.crash-utility.osci.io
> Message-ID:
> <
> cahs3rmxjg6oxb_zmgnr60kripoxo9tnb_63k+rjjhfk1t7a...@mail.gmail.com>
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>
> Hi Lianbo & Tao
>
> Currently, gdb passthroughs of 'bt', 'frame', 'up', 'down',
> 'info, locals' don't work on arm64 machine enabled pauth.
> This is due to gdb not knowing the lr register real values
> to unwind the stack frames.
>
> ----------------------------
> gdb passthrough (eg. "bt") | |
> crash -------------------------> | |
> | gdb_interface |
> | |
> | |
> | ---------------------- |
> get_kernel_pac_mask | | | |
> crash_target<-------------------------+--| gdb | |
> --------------------------+->| | |
> arm64: CONFIG_ARM64_KERNELPACMASK| | | |
> other: ~0UL | | | |
> | ---------------------- |
> ----------------------------
>
> With the patch:
> crash> gdb bt
> #0 __switch_to (prev=prev@entry=0xffffff8001af92c0,
> next=next@entry=0xffffff889da7a580)
> at /proc/self/cwd/common/arch/arm64/kernel/process.c:569
> #1 0xffffffd3602132c0 in context_switch (rq=0xffffff8a7295a080,
> prev=0xffffff8001af92c0, next=0xffffff889da7a580, rf=<optimized out>) at
> /proc/self/cwd/common/kernel/sched/core.c:5515
> #2 __schedule (sched_mode=<optimized out>, sched_mode@entry
> =2147859424)
> at /proc/self/cwd/common/kernel/sched/core.c:6843
> #3 0xffffffd3602136d8 in schedule () at
> /proc/self/cwd/common/kernel/sched/core.c:6917
> ...
>
> Without the patch:
> crash> gdb bt
> #0 __switch_to (prev=0xffffff8001af92c0, next=0xffffff889da7a580) at
> /proc/self/cwd/common/arch/arm64/kernel/process.c:569
> #1 0x9fc5c5d3602132c0 in ?? ()
> Backtrace stopped: previous frame identical to this frame (corrupt
> stack?)
>
> Signed-off-by: Guanyou.Chen <chenguan...@xiaomi.com>
> ---
> gdb-10.2.patch | 24 ++++++++++++++++++++++++
> gdb_interface.c | 11 +++++++++++
> 2 files changed, 35 insertions(+)
>
> diff --git a/gdb-10.2.patch b/gdb-10.2.patch
> index c867660..4c13a6b 100644
> --- a/gdb-10.2.patch
> +++ b/gdb-10.2.patch
> @@ -16216,3 +16216,27 @@ exit 0
> printf_filtered (_("Backtrace stopped: %s\n"),
> frame_stop_reason_string (trailing));
> }
> +--- gdb-10.2/gdb/frame.c.orig
> ++++ gdb-10.2/gdb/frame.c
> +@@ -944,6 +944,10 @@ frame_find_by_id (struct frame_id id)
> + return NULL;
> + }
> +
> ++#ifdef CRASH_MERGE
> ++extern "C" unsigned long crash_get_kernel_pac_mask(void);
> ++#endif
> ++
> + static CORE_ADDR
> + frame_unwind_pc (frame_info_ptr this_frame)
> + {
> +@@ -974,6 +978,10 @@ frame_unwind_pc (struct frame_info_ptr *this_frame)
> + try
> + {
> + pc = gdbarch_unwind_pc (prev_gdbarch, this_frame);
> ++#ifdef CRASH_MERGE
> ++ CORE_ADDR mask = crash_get_kernel_pac_mask();
> ++ pc |= mask;
>
Can you help double check if a sanity check needs to be added? I saw the
value 'pc|mask' is always checked in crash code as below:
...
LR = regs->regs[30];
if (is_kernel_text (LR | ms->CONFIG_ARM64_KERNELPACMASK))
LR |= ms->CONFIG_ARM64_KERNELPACMASK;
...
if yes, the value pc can be passed as an argument in
crash_get_kernel_pac_mask(), and then deal with this one.
> ++#endif
> + pc_p = true;
> + }
> + catch (const gdb_exception_error &ex)
> diff --git a/gdb_interface.c b/gdb_interface.c
> index 315711e..765dafe 100644
> --- a/gdb_interface.c
> +++ b/gdb_interface.c
> @@ -1083,3 +1083,14 @@ int crash_get_current_task_reg (int regno, const
> char *regname,
> return machdep->get_current_task_reg(regno, regname, regsize, value);
> }
>
> +/* arm64 kernel lr pac mask */
> +unsigned long crash_get_kernel_pac_mask(void);
> +unsigned long crash_get_kernel_pac_mask(void)
> +{
> +#ifdef ARM64
> + struct machine_specific *ms = machdep->machspec;
> + return ms->CONFIG_ARM64_KERNELPACMASK;
> +#else
> + return ~0UL;
>
The "~0UL" is 0xFFFFFFFFFFFFFFFF, is this expected? Or do you want it to
overflow?
++ pc |= mask;
It probably has the same result, but the "return 0UL" should be more
readable. Please see kernel code:
vmcoreinfo_append_str("NUMBER(KERNELPACMASK)=0x%llx\n",
system_supports_address_auth() ?
ptrauth_kernel_pac_mask() :
0);
BTW: I cannot apply your patch with git command, and ran into some issues,
probably it is a coding issue.
Thanks
Lianbo
> +#endif /* !ARM64 */
> +}
> --
> 2.34.1
>
> Thanks,
> Guanyou
>
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