From: Maninder Singh <maninder1.s@xxxxxxxxxxx> Subject: arm: print alloc free paths for address in registers In case of a use after free kernel oops, the freeing 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. e.g. in the below issue register r6 belongs to slab, and a use after free issue occurred on one of its dereferenced 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 Link: https://lkml.kernel.org/r/1615891032-29160-3-git-send-email-maninder1.s@xxxxxxxxxxx Co-developed-by: Vaneet Narang <v.narang@xxxxxxxxxxx> Signed-off-by: Vaneet Narang <v.narang@xxxxxxxxxxx> Signed-off-by: Maninder Singh <maninder1.s@xxxxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Christoph Lameter <cl@xxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Dmitry Safonov <0x7f454c46@xxxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx> Cc: Pekka Enberg <penberg@xxxxxxxxxx> Cc: Russell King <linux@xxxxxxxxxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- arch/arm/include/asm/bug.h | 1 + arch/arm/kernel/process.c | 11 +++++++++++ arch/arm/kernel/traps.c | 1 + 3 files changed, 13 insertions(+) --- a/arch/arm/include/asm/bug.h~arm-print-alloc-free-paths-for-address-in-registers +++ a/arch/arm/include/asm/bug.h @@ -88,5 +88,6 @@ extern asmlinkage void c_backtrace(unsig 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 --- a/arch/arm/kernel/process.c~arm-print-alloc-free-paths-for-address-in-registers +++ a/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; --- a/arch/arm/kernel/traps.c~arm-print-alloc-free-paths-for-address-in-registers +++ a/arch/arm/kernel/traps.c @@ -287,6 +287,7 @@ static int __die(const char *str, int er 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)); _
