Commit f8c26027 authored Jun 25, 2021 by Vasily Gorbik Committed by Heiko Carstens Jul 15, 2021

s390/ftrace: fix ftrace_update_ftrace_func implementation



s390 enforces DYNAMIC_FTRACE if FUNCTION_TRACER is selected.
At the same time implementation of ftrace_caller is not compliant with
HAVE_DYNAMIC_FTRACE since it doesn't provide implementation of
ftrace_update_ftrace_func() and calls ftrace_trace_function() directly.

The subtle difference is that during ftrace code patching ftrace
replaces function tracer via ftrace_update_ftrace_func() and activates
it back afterwards. Unexpected direct calls to ftrace_trace_function()
during ftrace code patching leads to nullptr-dereferences when tracing
is activated for one of functions which are used during code patching.
Those function currently are:
copy_from_kernel_nofault()
copy_from_kernel_nofault_allowed()
preempt_count_sub() [with debug_defconfig]
preempt_count_add() [with debug_defconfig]

Corresponding KASAN report:
 BUG: KASAN: nullptr-dereference in function_trace_call+0x316/0x3b0
 Read of size 4 at addr 0000000000001e08 by task migration/0/15

 CPU: 0 PID: 15 Comm: migration/0 Tainted: G B 5.13.0-41423-g08316af3644d
 Hardware name: IBM 3906 M04 704 (LPAR)
 Stopper: multi_cpu_stop+0x0/0x3e0 <- stop_machine_cpuslocked+0x1e4/0x218
 Call Trace:
  [<0000000001f77caa>] show_stack+0x16a/0x1d0
  [<0000000001f8de42>] dump_stack+0x15a/0x1b0
  [<0000000001f81d56>] print_address_description.constprop.0+0x66/0x2e0
  [<000000000082b0ca>] kasan_report+0x152/0x1c0
  [<00000000004cfd8e>] function_trace_call+0x316/0x3b0
  [<0000000001fb7082>] ftrace_caller+0x7a/0x7e
  [<00000000006bb3e6>] copy_from_kernel_nofault_allowed+0x6/0x10
  [<00000000006bb42e>] copy_from_kernel_nofault+0x3e/0xd0
  [<000000000014605c>] ftrace_make_call+0xb4/0x1f8
  [<000000000047a1b4>] ftrace_replace_code+0x134/0x1d8
  [<000000000047a6e0>] ftrace_modify_all_code+0x120/0x1d0
  [<000000000047a7ec>] __ftrace_modify_code+0x5c/0x78
  [<000000000042395c>] multi_cpu_stop+0x224/0x3e0
  [<0000000000423212>] cpu_stopper_thread+0x33a/0x5a0
  [<0000000000243ff2>] smpboot_thread_fn+0x302/0x708
  [<00000000002329ea>] kthread+0x342/0x408
  [<00000000001066b2>] __ret_from_fork+0x92/0xf0
  [<0000000001fb57fa>] ret_from_fork+0xa/0x30

 The buggy address belongs to the page:
 page:(____ptrval____) refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1
 flags: 0x1ffff00000001000(reserved|node=0|zone=0|lastcpupid=0x1ffff)
 raw: 1ffff00000001000 0000040000000048 0000040000000048 0000000000000000
 raw: 0000000000000000 0000000000000000 ffffffff00000001 0000000000000000
 page dumped because: kasan: bad access detected

 Memory state around the buggy address:
  0000000000001d00: f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7
  0000000000001d80: f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7
 >0000000000001e00: f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7
                       ^
  0000000000001e80: f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7
  0000000000001f00: f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7
 ==================================================================

To fix that introduce ftrace_func callback to be called from
ftrace_caller and update it in ftrace_update_ftrace_func().

Fixes: 4cc9bed0 ("[S390] cleanup ftrace backend functions")
Cc: stable@vger.kernel.org
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

parent c30e5e9f

arch/s390/include/asm/ftrace.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -19,6 +19,7 @@ void ftrace_caller(void);

		extern char ftrace_graph_caller_end;
		extern unsigned long ftrace_plt;
		extern void *ftrace_func;

		struct dyn_arch_ftrace { };

arch/s390/kernel/ftrace.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -40,6 +40,7 @@
		* trampoline (ftrace_plt), which clobbers also r1.
		*/

		void *ftrace_func __read_mostly = ftrace_stub;
		unsigned long ftrace_plt;

		int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
		@@ -85,6 +86,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)

		int ftrace_update_ftrace_func(ftrace_func_t func)
		{
		ftrace_func = func;
		return 0;
		}

arch/s390/kernel/mcount.S

+2 −2

Original line number	Diff line number	Diff line
		@@ -59,13 +59,13 @@ ENTRY(ftrace_caller)
		#ifdef CONFIG_HAVE_MARCH_Z196_FEATURES
		aghik %r2,%r0,-MCOUNT_INSN_SIZE
		lgrl %r4,function_trace_op
		lgrl %r1,ftrace_trace_function
		lgrl %r1,ftrace_func
		#else
		lgr %r2,%r0
		aghi %r2,-MCOUNT_INSN_SIZE
		larl %r4,function_trace_op
		lg %r4,0(%r4)
		larl %r1,ftrace_trace_function
		larl %r1,ftrace_func
		lg %r1,0(%r1)
		#endif
		lgr %r3,%r14