Re: [PATCH] powerpc/ftrace: Ignore ftrace locations in exit text sections

Michael reported that we are seeing ftrace bug on bootup when KASAN
is
enabled, and if we are using -fpatchable-function-entry:

    ftrace: allocating 47780 entries in 18 pages
    ftrace-powerpc: 0xc0000000020b3d5c: No module provided for non-
kernel address
    ------------[ ftrace bug ]------------
    ftrace faulted on modifying
    [<c0000000020b3d5c>] 0xc0000000020b3d5c
    Initializing ftrace call sites
    ftrace record flags: 0
     (0)
     expected tramp: c00000000008cef4
    ------------[ cut here ]------------
    WARNING: CPU: 0 PID: 0 at kernel/trace/ftrace.c:2180
ftrace_bug+0x3c0/0x424
    Modules linked in:
    CPU: 0 PID: 0 Comm: swapper Not tainted 6.5.0-rc3-00120-
g0f71dcfb4aef #860
    Hardware name: IBM pSeries (emulated by qemu) POWER9 (raw)
0x4e1202 0xf000005 of:SLOF,HEAD hv:linux,kvm pSeries
    NIP:  c0000000003aa81c LR: c0000000003aa818 CTR: 0000000000000000
    REGS: c0000000033cfab0 TRAP: 0700   Not tainted  (6.5.0-rc3-
00120-g0f71dcfb4aef)
    MSR:  8000000002021033 <SF,VEC,ME,IR,DR,RI,LE>  CR: 28028240 
XER: 00000000
    CFAR: c0000000002781a8 IRQMASK: 3
    ...
    NIP [c0000000003aa81c] ftrace_bug+0x3c0/0x424
    LR [c0000000003aa818] ftrace_bug+0x3bc/0x424
    Call Trace:
     ftrace_bug+0x3bc/0x424 (unreliable)
     ftrace_process_locs+0x5f4/0x8a0
     ftrace_init+0xc0/0x1d0
     start_kernel+0x1d8/0x484

With CONFIG_FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY=y and
CONFIG_KASAN=y, compiler emits nops in functions that it generates
for
registering and unregistering global variables (unlike with -pg and
-mprofile-kernel where calls to _mcount() are not generated in those
functions). Those functions then end up in INIT_TEXT and EXIT_TEXT
respectively. We don't expect to see any profiled functions in
EXIT_TEXT, so ftrace_init_nop() assumes that all addresses that
aren't
in the core kernel text belongs to a module. Since these functions do
not match that criteria, we see the above bug.

Address this by having ftrace ignore all locations in the text exit
sections of vmlinux.

Fixes: 0f71dcfb4aef ("powerpc/ftrace: Add support for -fpatchable-
function-entry")
Cc: stable@vger.kernel.org
Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Naveen N Rao <naveen@kernel.org>
---
 arch/powerpc/include/asm/ftrace.h   |  9 +--------
 arch/powerpc/include/asm/sections.h |  1 +
 arch/powerpc/kernel/trace/ftrace.c  | 12 ++++++++++++
 arch/powerpc/kernel/vmlinux.lds.S   |  2 ++
 4 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/include/asm/ftrace.h

b/arch/powerpc/include/asm/ftrace.h
index 1ebd2ca97f12..d6babd083202 100644

--- a/arch/powerpc/include/asm/ftrace.h
+++ b/arch/powerpc/include/asm/ftrace.h

@@ -20,14 +20,7 @@

 #ifndef __ASSEMBLY__
 extern void _mcount(void);
 
-static inline unsigned long ftrace_call_adjust(unsigned long addr)
-{
-	if (IS_ENABLED(CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY))
-		addr += MCOUNT_INSN_SIZE;
-
-	return addr;
-}
-
+unsigned long ftrace_call_adjust(unsigned long addr);
 unsigned long prepare_ftrace_return(unsigned long parent, unsigned
long ip,
 				    unsigned long sp);
 

diff --git a/arch/powerpc/include/asm/sections.h

b/arch/powerpc/include/asm/sections.h
index ea26665f82cf..d389dcecdb0b 100644

--- a/arch/powerpc/include/asm/sections.h
+++ b/arch/powerpc/include/asm/sections.h

@@ -14,6 +14,7 @@ typedef struct func_desc func_desc_t;

 
 extern char __head_end[];
 extern char __srwx_boundary[];
+extern char _sexittext[], _eexittext[];
 
 /* Patch sites */
 extern s32 patch__call_flush_branch_caches1;

diff --git a/arch/powerpc/kernel/trace/ftrace.c

b/arch/powerpc/kernel/trace/ftrace.c
index 82010629cf88..b5efd8d7bc01 100644

--- a/arch/powerpc/kernel/trace/ftrace.c
+++ b/arch/powerpc/kernel/trace/ftrace.c

@@ -27,10 +27,22 @@

 #include <asm/ftrace.h>
 #include <asm/syscall.h>
 #include <asm/inst.h>
+#include <asm/sections.h>
 
 #define	NUM_FTRACE_TRAMPS	2
 static unsigned long ftrace_tramps[NUM_FTRACE_TRAMPS];
 
+unsigned long ftrace_call_adjust(unsigned long addr)
+{
+	if (addr >= (unsigned long)_sexittext && addr < (unsigned
long)_eexittext)
+		return 0;
+
+	if (IS_ENABLED(CONFIG_ARCH_USING_PATCHABLE_FUNCTION_ENTRY))
+		addr += MCOUNT_INSN_SIZE;
+
+	return addr;
+}
+
 static ppc_inst_t ftrace_create_branch_inst(unsigned long ip,
unsigned long addr, int link)
 {
 	ppc_inst_t op;

diff --git a/arch/powerpc/kernel/vmlinux.lds.S

b/arch/powerpc/kernel/vmlinux.lds.S
index 1c5970df3233..9c376ae6857d 100644

--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S

@@ -281,7 +281,9 @@ SECTIONS

 	 * to deal with references from __bug_table
 	 */
 	.exit.text : AT(ADDR(.exit.text) - LOAD_OFFSET) {
+		_sexittext = .;
 		EXIT_TEXT
+		_eexittext = .;
 	}
 
 	. = ALIGN(PAGE_SIZE);

base-commit: 4ef8376c466ae8b03e632dd8eca1e44315f7dd61