From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
For the most part ftrace uses text poking and can handle ROX memory.
The only place that requires writable memory is create_trampoline() that
updates the allocated memory and in the end makes it ROX.
Use execmem_alloc_rw() in x86::ftrace::alloc_tramp() and enable ROX cache
for EXECMEM_FTRACE when configuration and CPU features allow that.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
arch/x86/kernel/ftrace.c | 2 +-
arch/x86/mm/init.c | 9 ++++++++-
2 files changed, 9 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 252e82bcfd2f..4450acec9390 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -263,7 +263,7 @@ void arch_ftrace_update_code(int command)
static inline void *alloc_tramp(unsigned long size)
{
- return execmem_alloc(EXECMEM_FTRACE, size);
+ return execmem_alloc_rw(EXECMEM_FTRACE, size);
}
static inline void tramp_free(void *tramp)
{
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 442fafd8ff52..bb57e93b4caf 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -1105,7 +1105,14 @@ struct execmem_info __init *execmem_arch_setup(void)
.pgprot = PAGE_KERNEL_ROX,
.alignment = MODULE_ALIGN,
},
- [EXECMEM_FTRACE ... EXECMEM_BPF] = {
+ [EXECMEM_FTRACE] = {
+ .flags = flags,
+ .start = start,
+ .end = MODULES_END,
+ .pgprot = pgprot,
+ .alignment = MODULE_ALIGN,
+ },
+ [EXECMEM_BPF] = {
.flags = EXECMEM_KASAN_SHADOW,
.start = start,
.end = MODULES_END,
--
2.47.2On Sun, 13 Jul 2025 10:17:30 +0300
Mike Rapoport <rppt@kernel.org> wrote:
> From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
>
> For the most part ftrace uses text poking and can handle ROX memory.
> The only place that requires writable memory is create_trampoline() that
> updates the allocated memory and in the end makes it ROX.
>
> Use execmem_alloc_rw() in x86::ftrace::alloc_tramp() and enable ROX cache
> for EXECMEM_FTRACE when configuration and CPU features allow that.
>
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
The "ftrace=function" kernel command line started crashing with v6.17-rc1,
and I bisected it down to this commit:
5d79c2be5081 ("x86/ftrace: enable EXECMEM_ROX_CACHE for ftrace allocations")
On boot I hit this:
[ 0.159269] BUG: kernel NULL pointer dereference, address: 000000000000001c
[ 0.160254] #PF: supervisor read access in kernel mode
[ 0.160975] #PF: error_code(0x0000) - not-present page
[ 0.161697] PGD 0 P4D 0
[ 0.162055] Oops: Oops: 0000 [#1] SMP PTI
[ 0.162619] CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.17.0-rc2-test-00006-g48d06e78b7cb-dirty #9 PREEMPT(undef)
[ 0.164141] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 0.165439] RIP: 0010:kmem_cache_alloc_noprof (mm/slub.c:4237)
[ 0.166186] Code: 90 90 90 f3 0f 1e fa 0f 1f 44 00 00 55 48 89 e5 41 57 41 56 41 55 41 54 49 89 fc 53 48 83 e4 f0 48 83 ec 20 8b 05 c9 b6 7e 01 <44> 8b 77 1c 65 4c 8b 2d b5 ea 20 02 4c 89 6c 24 18 41 89 f5 21 f0
All code
========
0: 90 nop
1: 90 nop
2: 90 nop
3: f3 0f 1e fa endbr64
7: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
c: 55 push %rbp
d: 48 89 e5 mov %rsp,%rbp
10: 41 57 push %r15
12: 41 56 push %r14
14: 41 55 push %r13
16: 41 54 push %r12
18: 49 89 fc mov %rdi,%r12
1b: 53 push %rbx
1c: 48 83 e4 f0 and $0xfffffffffffffff0,%rsp
20: 48 83 ec 20 sub $0x20,%rsp
24: 8b 05 c9 b6 7e 01 mov 0x17eb6c9(%rip),%eax # 0x17eb6f3
2a:* 44 8b 77 1c mov 0x1c(%rdi),%r14d <-- trapping instruction
2e: 65 4c 8b 2d b5 ea 20 mov %gs:0x220eab5(%rip),%r13 # 0x220eaeb
35: 02
36: 4c 89 6c 24 18 mov %r13,0x18(%rsp)
3b: 41 89 f5 mov %esi,%r13d
3e: 21 f0 and %esi,%eax
Code starting with the faulting instruction
===========================================
0: 44 8b 77 1c mov 0x1c(%rdi),%r14d
4: 65 4c 8b 2d b5 ea 20 mov %gs:0x220eab5(%rip),%r13 # 0x220eac1
b: 02
c: 4c 89 6c 24 18 mov %r13,0x18(%rsp)
11: 41 89 f5 mov %esi,%r13d
14: 21 f0 and %esi,%eax
[ 0.168811] RSP: 0000:ffffffffb2e03b30 EFLAGS: 00010086
[ 0.169545] RAX: 0000000001fff33f RBX: 0000000000000000 RCX: 0000000000000000
[ 0.170544] RDX: 0000000000002800 RSI: 0000000000002800 RDI: 0000000000000000
[ 0.171554] RBP: ffffffffb2e03b80 R08: 0000000000000004 R09: ffffffffb2e03c90
[ 0.172549] R10: ffffffffb2e03c90 R11: 0000000000000000 R12: 0000000000000000
[ 0.173544] R13: ffffffffb2e03c90 R14: ffffffffb2e03c90 R15: 0000000000000001
[ 0.174542] FS: 0000000000000000(0000) GS:ffff9d2808114000(0000) knlGS:0000000000000000
[ 0.175684] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 0.176486] CR2: 000000000000001c CR3: 000000007264c001 CR4: 00000000000200b0
[ 0.177483] Call Trace:
[ 0.177828] <TASK>
[ 0.178123] mas_alloc_nodes (lib/maple_tree.c:176 (discriminator 2) lib/maple_tree.c:1255 (discriminator 2))
[ 0.178692] mas_store_gfp (lib/maple_tree.c:5468)
[ 0.179223] execmem_cache_add_locked (mm/execmem.c:207)
[ 0.179870] execmem_alloc (mm/execmem.c:213 mm/execmem.c:313 mm/execmem.c:335 mm/execmem.c:475)
[ 0.180397] ? ftrace_caller (arch/x86/kernel/ftrace_64.S:169)
[ 0.180922] ? __pfx_ftrace_caller (arch/x86/kernel/ftrace_64.S:158)
[ 0.181517] execmem_alloc_rw (mm/execmem.c:487)
[ 0.182052] arch_ftrace_update_trampoline (arch/x86/kernel/ftrace.c:266 arch/x86/kernel/ftrace.c:344 arch/x86/kernel/ftrace.c:474)
[ 0.182778] ? ftrace_caller_op_ptr (arch/x86/kernel/ftrace_64.S:182)
[ 0.183388] ftrace_update_trampoline (kernel/trace/ftrace.c:7947)
[ 0.184024] __register_ftrace_function (kernel/trace/ftrace.c:368)
[ 0.184682] ftrace_startup (kernel/trace/ftrace.c:3048)
[ 0.185205] ? __pfx_function_trace_call (kernel/trace/trace_functions.c:210)
[ 0.185877] register_ftrace_function_nolock (kernel/trace/ftrace.c:8717)
[ 0.186595] register_ftrace_function (kernel/trace/ftrace.c:8745)
[ 0.187254] ? __pfx_function_trace_call (kernel/trace/trace_functions.c:210)
[ 0.187924] function_trace_init (kernel/trace/trace_functions.c:170)
[ 0.188499] tracing_set_tracer (kernel/trace/trace.c:5916 kernel/trace/trace.c:6349)
[ 0.189088] register_tracer (kernel/trace/trace.c:2391)
[ 0.189642] early_trace_init (kernel/trace/trace.c:11075 kernel/trace/trace.c:11149)
[ 0.190204] start_kernel (init/main.c:970)
[ 0.190732] x86_64_start_reservations (arch/x86/kernel/head64.c:307)
[ 0.191381] x86_64_start_kernel (??:?)
[ 0.191955] common_startup_64 (arch/x86/kernel/head_64.S:419)
[ 0.192534] </TASK>
[ 0.192839] Modules linked in:
[ 0.193267] CR2: 000000000000001c
[ 0.193730] ---[ end trace 0000000000000000 ]---
-- Steve
On Wed, Aug 20, 2025 at 06:47:43PM -0400, Steven Rostedt wrote:
> On Sun, 13 Jul 2025 10:17:30 +0300
> Mike Rapoport <rppt@kernel.org> wrote:
>
> > From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
> >
> > For the most part ftrace uses text poking and can handle ROX memory.
> > The only place that requires writable memory is create_trampoline() that
> > updates the allocated memory and in the end makes it ROX.
> >
> > Use execmem_alloc_rw() in x86::ftrace::alloc_tramp() and enable ROX cache
> > for EXECMEM_FTRACE when configuration and CPU features allow that.
> >
> > Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> > ---
>
> The "ftrace=function" kernel command line started crashing with v6.17-rc1,
> and I bisected it down to this commit:
>
> 5d79c2be5081 ("x86/ftrace: enable EXECMEM_ROX_CACHE for ftrace allocations")
>
> On boot I hit this:
>
> [ 0.159269] BUG: kernel NULL pointer dereference, address: 000000000000001c
> [ 0.160254] #PF: supervisor read access in kernel mode
> [ 0.160975] #PF: error_code(0x0000) - not-present page
> [ 0.161697] PGD 0 P4D 0
> [ 0.162055] Oops: Oops: 0000 [#1] SMP PTI
> [ 0.162619] CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.17.0-rc2-test-00006-g48d06e78b7cb-dirty #9 PREEMPT(undef)
> [ 0.164141] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> [ 0.165439] RIP: 0010:kmem_cache_alloc_noprof (mm/slub.c:4237)
> [ 0.177483] Call Trace:
> [ 0.177828] <TASK>
> [ 0.178123] mas_alloc_nodes (lib/maple_tree.c:176 (discriminator 2) lib/maple_tree.c:1255 (discriminator 2))
> [ 0.178692] mas_store_gfp (lib/maple_tree.c:5468)
> [ 0.179223] execmem_cache_add_locked (mm/execmem.c:207)
> [ 0.179870] execmem_alloc (mm/execmem.c:213 mm/execmem.c:313 mm/execmem.c:335 mm/execmem.c:475)
> [ 0.180397] ? ftrace_caller (arch/x86/kernel/ftrace_64.S:169)
> [ 0.180922] ? __pfx_ftrace_caller (arch/x86/kernel/ftrace_64.S:158)
> [ 0.181517] execmem_alloc_rw (mm/execmem.c:487)
> [ 0.182052] arch_ftrace_update_trampoline (arch/x86/kernel/ftrace.c:266 arch/x86/kernel/ftrace.c:344 arch/x86/kernel/ftrace.c:474)
> [ 0.182778] ? ftrace_caller_op_ptr (arch/x86/kernel/ftrace_64.S:182)
> [ 0.183388] ftrace_update_trampoline (kernel/trace/ftrace.c:7947)
> [ 0.184024] __register_ftrace_function (kernel/trace/ftrace.c:368)
> [ 0.184682] ftrace_startup (kernel/trace/ftrace.c:3048)
> [ 0.185205] ? __pfx_function_trace_call (kernel/trace/trace_functions.c:210)
> [ 0.185877] register_ftrace_function_nolock (kernel/trace/ftrace.c:8717)
> [ 0.186595] register_ftrace_function (kernel/trace/ftrace.c:8745)
> [ 0.187254] ? __pfx_function_trace_call (kernel/trace/trace_functions.c:210)
> [ 0.187924] function_trace_init (kernel/trace/trace_functions.c:170)
> [ 0.188499] tracing_set_tracer (kernel/trace/trace.c:5916 kernel/trace/trace.c:6349)
> [ 0.189088] register_tracer (kernel/trace/trace.c:2391)
> [ 0.189642] early_trace_init (kernel/trace/trace.c:11075 kernel/trace/trace.c:11149)
> [ 0.190204] start_kernel (init/main.c:970)
> [ 0.190732] x86_64_start_reservations (arch/x86/kernel/head64.c:307)
> [ 0.191381] x86_64_start_kernel (??:?)
> [ 0.191955] common_startup_64 (arch/x86/kernel/head_64.S:419)
> [ 0.192534] </TASK>
> [ 0.192839] Modules linked in:
> [ 0.193267] CR2: 000000000000001c
> [ 0.193730] ---[ end trace 0000000000000000 ]---
maple tree is initialized after ftrace, so the patch below should fix it:
diff --git a/init/main.c b/init/main.c
index 0ee0ee7b7c2c..5753e9539ae6 100644
--- a/init/main.c
+++ b/init/main.c
@@ -956,6 +956,7 @@ void start_kernel(void)
sort_main_extable();
trap_init();
mm_core_init();
+ maple_tree_init();
poking_init();
ftrace_init();
@@ -973,7 +974,6 @@ void start_kernel(void)
"Interrupts were enabled *very* early, fixing it\n"))
local_irq_disable();
radix_tree_init();
- maple_tree_init();
/*
* Set up housekeeping before setting up workqueues to allow the unbound
> -- Steve
--
Sincerely yours,
Mike.
On Thu, 21 Aug 2025 09:11:46 +0300 Mike Rapoport <rppt@kernel.org> wrote: > maple tree is initialized after ftrace, so the patch below should fix it: > > diff --git a/init/main.c b/init/main.c > index 0ee0ee7b7c2c..5753e9539ae6 100644 > --- a/init/main.c > +++ b/init/main.c > @@ -956,6 +956,7 @@ void start_kernel(void) > sort_main_extable(); > trap_init(); > mm_core_init(); > + maple_tree_init(); > poking_init(); > ftrace_init(); > > @@ -973,7 +974,6 @@ void start_kernel(void) > "Interrupts were enabled *very* early, fixing it\n")) > local_irq_disable(); > radix_tree_init(); > - maple_tree_init(); > > /* > * Set up housekeeping before setting up workqueues to allow the unbound > Tested-by: Steven Rostedt (Google) <rostedt@goodmis.org> Thanks, -- Steve
On Sun, 13 Jul 2025 10:17:30 +0300 Mike Rapoport <rppt@kernel.org> wrote: > From: "Mike Rapoport (Microsoft)" <rppt@kernel.org> > > For the most part ftrace uses text poking and can handle ROX memory. > The only place that requires writable memory is create_trampoline() that > updates the allocated memory and in the end makes it ROX. > > Use execmem_alloc_rw() in x86::ftrace::alloc_tramp() and enable ROX cache > for EXECMEM_FTRACE when configuration and CPU features allow that. > > Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> > Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org> Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org> -- Steve
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