[PATCH 1/1] arm64: print alloc free paths for address in registers

[Maninder Singh]

In case of a use after free kernel OOPs, freed path of the object is
required to debug futher. In most of cases the object address is present
in one of the registers.

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

commit a02a25709155 ("mm/slub: add support for free path information of an object")
provides free path along with alloc path of object in mem_dump_obj().

Thus call it with register values same as in ARM with
commit 14c0508adcdb ("arm: print alloc free paths for address in registers")

e.g.  in the below issue register x20 belongs to slab, and a use after free
issue occurred on one of its dereferenced values:

[   19.516507] Unable to handle kernel paging request at virtual address 006b6b6b6b6b6b73
..
..
[   19.528784] Register x10 information: 0-page vmalloc region starting at 0xffff800011bb0000 allocated at paging_init+0x1d8/0x544
[   19.529143] Register x11 information: 0-page vmalloc region starting at 0xffff800011bb0000 allocated at paging_init+0x1d8/0x544
[   19.529513] Register x12 information: non-paged memory
..
[   19.544953] Register x20 information: slab kmalloc-128 start ffff0000c3a34280 data offset 128 pointer offset 0 size 128 allocated at meminfo_proc_show+0x44/0x588
[   19.545432]     ___slab_alloc+0x638/0x658
[   19.545576]     __slab_alloc.isra.0+0x2c/0x58
[   19.545728]     kmem_cache_alloc+0x584/0x598
[   19.545877]     meminfo_proc_show+0x44/0x588
[   19.546022]     seq_read_iter+0x258/0x460
[   19.546160]     proc_reg_read_iter+0x90/0xd0
[   19.546308]     generic_file_splice_read+0xd0/0x188
[   19.546474]     do_splice_to+0x90/0xe0
[   19.546609]     splice_direct_to_actor+0xbc/0x240
[   19.546768]     do_splice_direct+0x8c/0xe8
[   19.546911]     do_sendfile+0x2c4/0x500
[   19.547048]     __arm64_sys_sendfile64+0x160/0x168
[   19.547205]     el0_svc_common.constprop.0+0x60/0x120
[   19.547377]     do_el0_svc_compat+0x1c/0x40
[   19.547524]     el0_svc_compat+0x24/0x38
[   19.547660]     el0_sync_compat_handler+0x90/0x158
[   19.547821]  Free path:
[   19.547906]     __slab_free+0x3dc/0x538
[   19.548051]     kfree+0x2d8/0x310
[   19.548176]     meminfo_proc_show+0x60/0x588
[   19.548322]     seq_read_iter+0x258/0x460
[   19.548459]     proc_reg_read_iter+0x90/0xd0
[   19.548602]     generic_file_splice_read+0xd0/0x188
[   19.548761]     do_splice_to+0x90/0xe0
[   19.548889]     splice_direct_to_actor+0xbc/0x240
[   19.549040]     do_splice_direct+0x8c/0xe8
[   19.549183]     do_sendfile+0x2c4/0x500
[   19.549319]     __arm64_sys_sendfile64+0x160/0x168
[   19.549477]     el0_svc_common.constprop.0+0x60/0x120
[   19.549646]     do_el0_svc_compat+0x1c/0x40
[   19.549782]     el0_svc_compat+0x24/0x38
[   19.549913]     el0_sync_compat_handler+0x90/0x158
[   19.550067]     el0_sync_compat+0x174/0x180
..

Signed-off-by: Vaneet Narang <v.narang at samsung.com>
Signed-off-by: Maninder Singh <maninder1.s at samsung.com>
---
 arch/arm64/include/asm/system_misc.h |  1 +
 arch/arm64/kernel/process.c          | 11 +++++++++++
 arch/arm64/kernel/traps.c            |  1 +
 3 files changed, 13 insertions(+)

diff --git a/arch/arm64/include/asm/system_misc.h b/arch/arm64/include/asm/system_misc.h
index 673be2d1263c..84d5204cdb80 100644
--- a/arch/arm64/include/asm/system_misc.h
+++ b/arch/arm64/include/asm/system_misc.h
@@ -31,6 +31,7 @@ void hook_debug_fault_code(int nr, int (*fn)(unsigned long, unsigned int,
 
 struct mm_struct;
 extern void __show_regs(struct pt_regs *);
+extern void __show_regs_alloc_free(struct pt_regs *regs);
 
 extern void (*arm_pm_restart)(enum reboot_mode reboot_mode, const char *cmd);
 
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 325c83b1a24d..a21761cee3dc 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -304,6 +304,17 @@ void __show_regs(struct pt_regs *regs)
 	}
 }
 
+void __show_regs_alloc_free(struct pt_regs *regs)
+{
+	int i;
+
+	/* check for x0 - x29 only */
+	for (i = 0; i <= 29; i++) {
+		pr_alert("Register x%d information:", i);
+		mem_dump_obj((void *)regs->regs[i]);
+	}
+}
+
 void show_regs(struct pt_regs *regs)
 {
 	__show_regs(regs);
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index a05d34f0e82a..cb4858c6e57b 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -104,6 +104,7 @@ static int __die(const char *str, int err, struct pt_regs *regs)
 
 	print_modules();
 	show_regs(regs);
+	__show_regs_alloc_free(regs);
 
 	dump_kernel_instr(KERN_EMERG, regs);
 
-- 
2.17.1