[PATCH 1/1] arm64: Print slab alloc and free paths for addresses in registers

[Onkarnath]

When debugging use-after-free kernel oopses, knowing the allocation and
freeing paths of an object is crucial. Like arm this patch enhances arm64
debugging by checking if register addresses belong to a slab and printing
their corresponding alloc and free paths.

For example x21 prints alloc and free path:

pc : crash_init+0x44/0x64 [crash]
lr : crash_init+0x34/0x64 [crash]
.....
Register x21 information: slab task_struct start ffff0000c3cc7000 data offset 64 pointer offset 0 size 3904 allocated at copy_process+0x1ac/0x14a4
    kmem_cache_alloc_node_noprof+0x208/0x4a8
    copy_process+0x1ac/0x14a4
    kernel_clone+0x70/0x380
    __arm64_sys_fork+0x40/0x7c
    invoke_syscall+0x48/0x104
    el0_svc_common.constprop.0+0x40/0xe0
    do_el0_svc_compat+0x1c/0x34
    el0_svc_compat+0x2c/0x90
    el0t_32_sync_handler+0x88/0xac
    el0t_32_sync+0x19c/0x1a0
 Free path:
    kmem_cache_free+0x3c0/0x430
    free_task+0x54/0x80
    __put_task_struct+0x100/0x15c
    __put_task_struct_rcu_cb+0x14/0x20
    rcu_core+0x264/0x680
    rcu_core_si+0x10/0x1c
    handle_softirqs+0x100/0x244
    __do_softirq+0x14/0x20

Co-developed-by: Sarvesh Kadam <s.kadam at samsung.com>
Signed-off-by: Sarvesh Kadam <s.kadam at samsung.com>
Signed-off-by: Onkarnath <onkarnath.1 at samsung.com>
---
 arch/arm64/include/asm/system_misc.h |  1 +
 arch/arm64/kernel/process.c          | 11 +++++++++++
 arch/arm64/kernel/traps.c            |  2 +-
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/system_misc.h b/arch/arm64/include/asm/system_misc.h
index d316a804eb38..9cb9749d8853 100644
--- a/arch/arm64/include/asm/system_misc.h
+++ b/arch/arm64/include/asm/system_misc.h
@@ -27,6 +27,7 @@ void arm64_notify_die(const char *str, struct pt_regs *regs,
 
 struct mm_struct;
 extern void __show_regs(struct pt_regs *);
+extern void __show_regs_alloc_free(struct pt_regs *regs);
 
 #endif	/* __ASSEMBLER__ */
 
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index fba7ca102a8c..7738ec8e5cd5 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -199,6 +199,17 @@ static void print_pstate(struct pt_regs *regs)
 	}
 }
 
+void __show_regs_alloc_free(struct pt_regs *regs)
+{
+	int i;
+
+	/* check for x0 - x31 only */
+	for (i = 0; i < 31; i++) {
+		pr_alert("Register x%d information:", i);
+		mem_dump_obj((void *)regs->regs[i]);
+	}
+}
+
 void __show_regs(struct pt_regs *regs)
 {
 	int i, top_reg;
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 914282016069..3b01379b8880 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -189,7 +189,7 @@ static int __die(const char *str, long err, struct pt_regs *regs)
 
 	print_modules();
 	show_regs(regs);
-
+	__show_regs_alloc_free(regs);
 	if (user_mode(regs))
 		return ret;
 
-- 
2.25.1