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Subject[PATCH] ARM: ftrace/recordmcount: filter relocation types
Date
Scenario 1, ARMv7:
==================

If code in arch/arm/kernel/ftrace.c would operate on mcount() pointer
the following may be generated:

00000230 <prealloc_fixed_plts>:
230: b5f8 push {r3, r4, r5, r6, r7, lr}
232: b500 push {lr}
234: f7ff fffe bl 0 <__gnu_mcount_nc>
234: R_ARM_THM_CALL __gnu_mcount_nc
238: f240 0600 movw r6, #0
238: R_ARM_THM_MOVW_ABS_NC __gnu_mcount_nc
23c: f8d0 1180 ldr.w r1, [r0, #384] ; 0x180

FTRACE currently is not able to deal with it:

WARNING: CPU: 0 PID: 0 at .../kernel/trace/ftrace.c:1979 ftrace_bug+0x1ad/0x230()
...
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.4.116-... #1
...
[<c0314e3d>] (unwind_backtrace) from [<c03115e9>] (show_stack+0x11/0x14)
[<c03115e9>] (show_stack) from [<c051a7f1>] (dump_stack+0x81/0xa8)
[<c051a7f1>] (dump_stack) from [<c0321c5d>] (warn_slowpath_common+0x69/0x90)
[<c0321c5d>] (warn_slowpath_common) from [<c0321cf3>] (warn_slowpath_null+0x17/0x1c)
[<c0321cf3>] (warn_slowpath_null) from [<c038ee9d>] (ftrace_bug+0x1ad/0x230)
[<c038ee9d>] (ftrace_bug) from [<c038f1f9>] (ftrace_process_locs+0x27d/0x444)
[<c038f1f9>] (ftrace_process_locs) from [<c08915bd>] (ftrace_init+0x91/0xe8)
[<c08915bd>] (ftrace_init) from [<c0885a67>] (start_kernel+0x34b/0x358)
[<c0885a67>] (start_kernel) from [<00308095>] (0x308095)
---[ end trace cb88537fdc8fa200 ]---
ftrace failed to modify [<c031266c>] prealloc_fixed_plts+0x8/0x60
actual: 44:f2:e1:36
ftrace record flags: 0
(0) expected tramp: c03143e9

Scenario 2, ARMv4T:
===================

ftrace: allocating 14435 entries in 43 pages
------------[ cut here ]------------
WARNING: CPU: 0 PID: 0 at kernel/trace/ftrace.c:2029 ftrace_bug+0x204/0x310
CPU: 0 PID: 0 Comm: swapper Not tainted 4.19.5 #1
Hardware name: Cirrus Logic EDB9302 Evaluation Board
[<c0010a24>] (unwind_backtrace) from [<c000ecb0>] (show_stack+0x20/0x2c)
[<c000ecb0>] (show_stack) from [<c03c72e8>] (dump_stack+0x20/0x30)
[<c03c72e8>] (dump_stack) from [<c0021c18>] (__warn+0xdc/0x104)
[<c0021c18>] (__warn) from [<c0021d7c>] (warn_slowpath_null+0x4c/0x5c)
[<c0021d7c>] (warn_slowpath_null) from [<c0095360>] (ftrace_bug+0x204/0x310)
[<c0095360>] (ftrace_bug) from [<c04dabac>] (ftrace_init+0x3b4/0x4d4)
[<c04dabac>] (ftrace_init) from [<c04cef4c>] (start_kernel+0x20c/0x410)
[<c04cef4c>] (start_kernel) from [<00000000>] ( (null))
---[ end trace 0506a2f5dae6b341 ]---
ftrace failed to modify
[<c000c350>] perf_trace_sys_exit+0x5c/0xe8
actual: 1e:ff:2f:e1
Initializing ftrace call sites
ftrace record flags: 0
(0)
expected tramp: c000fb24

The analysis for this problem has been already performed previously,
refer to the link below.

Fix the above problems by allowing only selected reloc types in
__mcount_loc. The list itself comes from the legacy recordmcount.pl
script.

Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/lkml/56961010.6000806@pengutronix.de/
Fixes: ed60453fa8 ("ARM: 6511/1: ftrace: add ARM support for C version of recordmcount")
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
---
scripts/recordmcount.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)

diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
index 895c40e8679f..3b0dcf38fd8b 100644
--- a/scripts/recordmcount.c
+++ b/scripts/recordmcount.c
@@ -39,6 +39,10 @@
#define R_AARCH64_ABS64 257
#endif

+#define R_ARM_PC24 1
+#define R_ARM_THM_CALL 10
+#define R_ARM_CALL 28
+
static int fd_map; /* File descriptor for file being modified. */
static int mmap_failed; /* Boolean flag. */
static char gpfx; /* prefix for global symbol name (sometimes '_') */
@@ -414,6 +418,18 @@ is_mcounted_section_name(char const *const txtname)
#define RECORD_MCOUNT_64
#include "recordmcount.h"

+static int arm_is_fake_mcount(Elf32_Rel const *rp)
+{
+ switch (ELF32_R_TYPE(w(rp->r_info))) {
+ case R_ARM_THM_CALL:
+ case R_ARM_CALL:
+ case R_ARM_PC24:
+ return 0;
+ }
+
+ return 1;
+}
+
/* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
* http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
* We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
@@ -515,6 +531,7 @@ do_file(char const *const fname)
altmcount = "__gnu_mcount_nc";
make_nop = make_nop_arm;
rel_type_nop = R_ARM_NONE;
+ is_fake_mcount32 = arm_is_fake_mcount;
break;
case EM_AARCH64:
reltype = R_AARCH64_ABS64;
--
2.19.2
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