[PATCH 3/3] arm: print alloc free paths for address in registers

[Maninder Singh]

In case of user after free kernel OOPs, free path of object
is required to debug futher.
And in most of cases object address is present in one of registers.

Thus check for register address and if it belongs to slab,
print its alloc and free path.

e.g. in below issue  register r6 belongs to slab, and user afree issue
occurred on one of its derefer values:

[   20.182197] Unable to handle kernel paging request at virtual address 6b6b6b6f
....
[   20.185035] pc : [<c0538afc>]    lr : [<c0465674>]    psr: 60000013
[   20.185271] sp : c8927d40  ip : ffffefff  fp : c8aa8020
[   20.185462] r10: c8927e10  r9 : 00000001  r8 : 00400cc0
[   20.185674] r7 : 00000000  r6 : c8ab0180  r5 : c1804a80  r4 : c8aa8008
[   20.185924] r3 : c1a5661c  r2 : 00000000  r1 : 6b6b6b6b  r0 : c139bf48
.....
[   20.191499] Register r6 information: slab kmalloc-64 start c8ab0140 data offset 64 pointer offset 0 size 64 allocated at meminfo_proc_show+0x40/0x4fc
[   20.192078]     meminfo_proc_show+0x40/0x4fc
[   20.192263]     seq_read_iter+0x18c/0x4c4
[   20.192430]     proc_reg_read_iter+0x84/0xac
[   20.192617]     generic_file_splice_read+0xe8/0x17c
[   20.192816]     splice_direct_to_actor+0xb8/0x290
[   20.193008]     do_splice_direct+0xa0/0xe0
[   20.193185]     do_sendfile+0x2d0/0x438
[   20.193345]     sys_sendfile64+0x12c/0x140
[   20.193523]     ret_fast_syscall+0x0/0x58
[   20.193695]     0xbeeacde4
[   20.193822]  Free path:
[   20.193935]     meminfo_proc_show+0x5c/0x4fc
[   20.194115]     seq_read_iter+0x18c/0x4c4
[   20.194285]     proc_reg_read_iter+0x84/0xac
[   20.194475]     generic_file_splice_read+0xe8/0x17c
[   20.194685]     splice_direct_to_actor+0xb8/0x290
[   20.194870]     do_splice_direct+0xa0/0xe0
[   20.195014]     do_sendfile+0x2d0/0x438
[   20.195174]     sys_sendfile64+0x12c/0x140
[   20.195336]     ret_fast_syscall+0x0/0x58
[   20.195491]     0xbeeacde4

Co-developed-by: Vaneet Narang <v.narang@xxxxxxxxxxx>
Signed-off-by: Vaneet Narang <v.narang@xxxxxxxxxxx>
Signed-off-by: Maninder Singh <maninder1.s@xxxxxxxxxxx>
---
 arch/arm/include/asm/bug.h |  1 +
 arch/arm/kernel/process.c  | 11 +++++++++++
 arch/arm/kernel/traps.c    |  1 +
 3 files changed, 13 insertions(+)

diff --git a/arch/arm/include/asm/bug.h b/arch/arm/include/asm/bug.h
index 673c7dd75ab9..ba8d9d7d242b 100644
--- a/arch/arm/include/asm/bug.h
+++ b/arch/arm/include/asm/bug.h
@@ -88,5 +88,6 @@ extern asmlinkage void c_backtrace(unsigned long fp, int pmode,
 struct mm_struct;
 void show_pte(const char *lvl, struct mm_struct *mm, unsigned long addr);
 extern void __show_regs(struct pt_regs *);
+extern void __show_regs_alloc_free(struct pt_regs *regs);
 
 #endif
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 5199a2bb4111..249dd285c4d8 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -92,6 +92,17 @@ void arch_cpu_idle_exit(void)
 	ledtrig_cpu(CPU_LED_IDLE_END);
 }
 
+void __show_regs_alloc_free(struct pt_regs *regs)
+{
+	int i;
+
+	/* check for r0 - r12 only */
+	for (i = 0; i < 13; i++) {
+		pr_alert("Register r%d information:", i);
+		mem_dump_obj((void *)regs->uregs[i]);
+	}
+}
+
 void __show_regs(struct pt_regs *regs)
 {
 	unsigned long flags;
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 17d5a785df28..64308e3a5d0c 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -287,6 +287,7 @@ static int __die(const char *str, int err, struct pt_regs *regs)
 
 	print_modules();
 	__show_regs(regs);
+	__show_regs_alloc_free(regs);
 	pr_emerg("Process %.*s (pid: %d, stack limit = 0x%p)\n",
 		 TASK_COMM_LEN, tsk->comm, task_pid_nr(tsk), end_of_stack(tsk));
 
-- 
2.17.1