arch/x86/kernel/alternative.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
Fei has reported that KASAN triggers during apply_alternatives() on
5-level paging machine:
BUG: KASAN: out-of-bounds in rcu_is_watching (./arch/x86/include/asm/atomic.h:23 ./include/linux/atomic/atomic-arch-fallback.h:444 ./include/linux/context_tracking.h:122 kernel/rcu/tree.c:699)
Read of size 4 at addr ff110003ee6419a0 by task swapper/0/0
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.6.0-rc5 #12
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
Call Trace:
<TASK>
dump_stack_lvl (lib/dump_stack.c:107)
print_report (mm/kasan/report.c:365 mm/kasan/report.c:475)
? __phys_addr (arch/x86/mm/physaddr.h:7 arch/x86/mm/physaddr.c:28)
? kasan_addr_to_slab (./include/linux/mm.h:1265 (discriminator 1) mm/kasan/../slab.h:213 (discriminator 1) mm/kasan/common.c:36 (discriminator 1))
kasan_report (mm/kasan/report.c:590)
? rcu_is_watching (./arch/x86/include/asm/atomic.h:23 ./include/linux/atomic/atomic-arch-fallback.h:444 ./include/linux/context_tracking.h:122 kernel/rcu/tree.c:699)
? rcu_is_watching (./arch/x86/include/asm/atomic.h:23 ./include/linux/atomic/atomic-arch-fallback.h:444 ./include/linux/context_tracking.h:122 kernel/rcu/tree.c:699)
? apply_alternatives (arch/x86/kernel/alternative.c:415 (discriminator 1))
__asan_load4 (mm/kasan/generic.c:259)
rcu_is_watching (./arch/x86/include/asm/atomic.h:23 ./include/linux/atomic/atomic-arch-fallback.h:444 ./include/linux/context_tracking.h:122 kernel/rcu/tree.c:699)
? text_poke_early (./arch/x86/include/asm/irqflags.h:42 ./arch/x86/include/asm/irqflags.h:77 ./arch/x86/include/asm/irqflags.h:135 arch/x86/kernel/alternative.c:1675)
trace_hardirqs_on (./include/trace/events/preemptirq.h:40 (discriminator 2) ./include/trace/events/preemptirq.h:40 (discriminator 2) kernel/trace/trace_preemptirq.c:56 (discriminator 2))
? __asan_load4 (./arch/x86/include/asm/cpufeature.h:171 mm/kasan/kasan.h:306 mm/kasan/generic.c:175 mm/kasan/generic.c:259)
text_poke_early (./arch/x86/include/asm/irqflags.h:42 ./arch/x86/include/asm/irqflags.h:77 ./arch/x86/include/asm/irqflags.h:135 arch/x86/kernel/alternative.c:1675)
apply_alternatives (arch/x86/kernel/alternative.c:415 (discriminator 1))
? __asan_load4 (./arch/x86/include/asm/cpufeature.h:171 mm/kasan/kasan.h:306 mm/kasan/generic.c:175 mm/kasan/generic.c:259)
? __pfx_apply_alternatives (arch/x86/kernel/alternative.c:400)
? __pfx_apply_returns (arch/x86/kernel/alternative.c:720)
? __this_cpu_preempt_check (lib/smp_processor_id.c:67)
? _sub_I_65535_1 (init/main.c:1573)
? int3_selftest_ip (arch/x86/kernel/alternative.c:1496)
? __pfx_int3_selftest (arch/x86/kernel/alternative.c:1496)
? lockdep_hardirqs_on (kernel/locking/lockdep.c:4422)
? fpu__init_cpu_generic (./arch/x86/include/asm/irqflags.h:42 ./arch/x86/include/asm/irqflags.h:77 ./arch/x86/include/asm/irqflags.h:135 ./arch/x86/include/asm/tlbflush.h:47 arch/x86/kernel/fpu/init.c:30)
alternative_instructions (arch/x86/kernel/alternative.c:1618)
arch_cpu_finalize_init (arch/x86/kernel/cpu/common.c:2404)
start_kernel (init/main.c:1037)
x86_64_start_reservations (arch/x86/kernel/head64.c:544)
x86_64_start_kernel (arch/x86/kernel/head64.c:486 (discriminator 5))
secondary_startup_64_no_verify (arch/x86/kernel/head_64.S:433)
</TASK>
The buggy address belongs to the physical page:
page:(____ptrval____) refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x3ee641
flags: 0x20000000004000(reserved|node=0|zone=2)
page_type: 0xffffffff()
raw: 0020000000004000 ffd400000fb99048 ffd400000fb99048 0000000000000000
raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
Memory state around the buggy address:
ff110003ee641880: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ff110003ee641900: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ff110003ee641980: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
^
ff110003ee641a00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ff110003ee641a80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
On machines with 5-level paging, cpu_feature_enabled(X86_FEATURE_LA57)
got patched. It includes KASAN code, where KASAN_SHADOW_START depends on
__VIRTUAL_MASK_SHIFT, which is defined with the cpu_feature_enabled().
KASAN gets confused when apply_alternatives() patches the
KASAN_SHADOW_START users. A test patch that makes KASAN_SHADOW_START
static, by replacing __VIRTUAL_MASK_SHIFT with 56, fixes the issue.
Disable KASAN while kernel patches alternatives.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: Fei Yang <fei.yang@intel.com>
Fixes: 6657fca06e3f ("x86/mm: Allow to boot without LA57 if CONFIG_X86_5LEVEL=y")
Cc: stable@vger.kernel.org
---
v2:
- Move kasan_disable/_enable_current() to cover whole loop, not only
text_poke_early();
- Adjust commit message.
---
arch/x86/kernel/alternative.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 517ee01503be..b4cc4d7c0825 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -403,6 +403,17 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
u8 insn_buff[MAX_PATCH_LEN];
DPRINTK(ALT, "alt table %px, -> %px", start, end);
+
+ /*
+ * In the case CONFIG_X86_5LEVEL=y, KASAN_SHADOW_START is defined using
+ * cpu_feature_enabled(X86_FEATURE_LA57) and is therefore patched here.
+ * During the process, KASAN becomes confused and triggers
+ * a false-positive out-of-bound report.
+ *
+ * Disable KASAN until the patching is complete.
+ */
+ kasan_disable_current();
+
/*
* The scan order should be from start to end. A later scanned
* alternative code can overwrite previously scanned alternative code.
@@ -452,6 +463,8 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
text_poke_early(instr, insn_buff, insn_buff_sz);
}
+
+ kasan_enable_current();
}
static inline bool is_jcc32(struct insn *insn)
--
2.41.0On Wed, Oct 11, 2023 at 09:58:49AM +0300, Kirill A. Shutemov wrote:
> Fei has reported that KASAN triggers during apply_alternatives() on
> 5-level paging machine:
>
Urgh @ KASAN splat, can't we summarize that?
>
> On machines with 5-level paging, cpu_feature_enabled(X86_FEATURE_LA57)
> got patched. It includes KASAN code, where KASAN_SHADOW_START depends on
> __VIRTUAL_MASK_SHIFT, which is defined with the cpu_feature_enabled().
>
> KASAN gets confused when apply_alternatives() patches the
> KASAN_SHADOW_START users. A test patch that makes KASAN_SHADOW_START
> static, by replacing __VIRTUAL_MASK_SHIFT with 56, fixes the issue.
>
> Disable KASAN while kernel patches alternatives.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Reported-by: Fei Yang <fei.yang@intel.com>
> Fixes: 6657fca06e3f ("x86/mm: Allow to boot without LA57 if CONFIG_X86_5LEVEL=y")
> Cc: stable@vger.kernel.org
> ---
>
> v2:
> - Move kasan_disable/_enable_current() to cover whole loop, not only
> text_poke_early();
> - Adjust commit message.
>
> ---
> arch/x86/kernel/alternative.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index 517ee01503be..b4cc4d7c0825 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -403,6 +403,17 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
> u8 insn_buff[MAX_PATCH_LEN];
>
> DPRINTK(ALT, "alt table %px, -> %px", start, end);
> +
> + /*
> + * In the case CONFIG_X86_5LEVEL=y, KASAN_SHADOW_START is defined using
> + * cpu_feature_enabled(X86_FEATURE_LA57) and is therefore patched here.
> + * During the process, KASAN becomes confused and triggers
because of partial LA57 convertion ..
> + * a false-positive out-of-bound report.
> + *
> + * Disable KASAN until the patching is complete.
> + */
> + kasan_disable_current();
> +
> /*
> * The scan order should be from start to end. A later scanned
> * alternative code can overwrite previously scanned alternative code.
> @@ -452,6 +463,8 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
>
> text_poke_early(instr, insn_buff, insn_buff_sz);
> }
> +
> + kasan_enable_current();
> }
Other than that, ACK.
On Wed, Oct 11, 2023 at 09:46:16AM +0200, Peter Zijlstra wrote: > On Wed, Oct 11, 2023 at 09:58:49AM +0300, Kirill A. Shutemov wrote: > > Fei has reported that KASAN triggers during apply_alternatives() on > > 5-level paging machine: > > > > Urgh @ KASAN splat, can't we summarize that? What about this? BUG: KASAN: out-of-bounds in rcu_is_watching Read of size 4 at addr ff110003ee6419a0 by task swapper/0/0 ... __asan_load4 rcu_is_watching ? text_poke_early trace_hardirqs_on ? __asan_load4 text_poke_early apply_alternatives ... Is it enough details or I overdid summarization? > > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > > index 517ee01503be..b4cc4d7c0825 100644 > > --- a/arch/x86/kernel/alternative.c > > +++ b/arch/x86/kernel/alternative.c > > @@ -403,6 +403,17 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start, > > u8 insn_buff[MAX_PATCH_LEN]; > > > > DPRINTK(ALT, "alt table %px, -> %px", start, end); > > + > > + /* > > + * In the case CONFIG_X86_5LEVEL=y, KASAN_SHADOW_START is defined using > > + * cpu_feature_enabled(X86_FEATURE_LA57) and is therefore patched here. > > + * During the process, KASAN becomes confused and triggers > > because of partial LA57 convertion .. > > > + * a false-positive out-of-bound report. > > + * > > + * Disable KASAN until the patching is complete. > > + */ > > + kasan_disable_current(); > > + > > /* /* * In the case CONFIG_X86_5LEVEL=y, KASAN_SHADOW_START is defined using * cpu_feature_enabled(X86_FEATURE_LA57) and is therefore patched here. * During the process, KASAN becomes confused seeing partial LA57 * conversion and triggers a false-positive out-of-bound report. * * Disable KASAN until the patching is complete. */ Looks good? If yes, I will submit v3 with your Ack. -- Kiryl Shutsemau / Kirill A. Shutemov
* Kirill A. Shutemov <kirill.shutemov@linux.intel.com> wrote: > On Wed, Oct 11, 2023 at 09:46:16AM +0200, Peter Zijlstra wrote: > > On Wed, Oct 11, 2023 at 09:58:49AM +0300, Kirill A. Shutemov wrote: > > > Fei has reported that KASAN triggers during apply_alternatives() on > > > 5-level paging machine: > > > > > > > Urgh @ KASAN splat, can't we summarize that? > > What about this? > > BUG: KASAN: out-of-bounds in rcu_is_watching > Read of size 4 at addr ff110003ee6419a0 by task swapper/0/0 > ... > __asan_load4 > rcu_is_watching > ? text_poke_early > trace_hardirqs_on > ? __asan_load4 > text_poke_early > apply_alternatives > ... > > Is it enough details or I overdid summarization? No, that's perfect IMO. I'd even leave out the unreliable '?' entries: > BUG: KASAN: out-of-bounds in rcu_is_watching > Read of size 4 at addr ff110003ee6419a0 by task swapper/0/0 > ... > __asan_load4 > rcu_is_watching > trace_hardirqs_on > text_poke_early > apply_alternatives > ... ... or so. > /* > * In the case CONFIG_X86_5LEVEL=y, KASAN_SHADOW_START is defined using > * cpu_feature_enabled(X86_FEATURE_LA57) and is therefore patched here. > * During the process, KASAN becomes confused seeing partial LA57 > * conversion and triggers a false-positive out-of-bound report. > * > * Disable KASAN until the patching is complete. > */ > > Looks good? LGTM. Thanks, Ingo
* Peter Zijlstra <peterz@infradead.org> wrote: > > DPRINTK(ALT, "alt table %px, -> %px", start, end); > > + > > + /* > > + * In the case CONFIG_X86_5LEVEL=y, KASAN_SHADOW_START is defined using > > + * cpu_feature_enabled(X86_FEATURE_LA57) and is therefore patched here. > > + * During the process, KASAN becomes confused and triggers > > because of partial LA57 convertion .. Not all LA57 related sites are patched yet at this point, and KASAN sees a weird & broken mixture of LA48 and LA57 runtime semantics, right? Ie. as far as KASAN is concerned, the LA48 -> LA57 behavioral switchover must be atomic, but during the kernel code patching process it isn't. Thanks, Ingo
On Wed, Oct 11, 2023 at 10:11:46AM +0200, Ingo Molnar wrote: > > * Peter Zijlstra <peterz@infradead.org> wrote: > > > > DPRINTK(ALT, "alt table %px, -> %px", start, end); > > > + > > > + /* > > > + * In the case CONFIG_X86_5LEVEL=y, KASAN_SHADOW_START is defined using > > > + * cpu_feature_enabled(X86_FEATURE_LA57) and is therefore patched here. > > > + * During the process, KASAN becomes confused and triggers > > > > because of partial LA57 convertion .. > > Not all LA57 related sites are patched yet at this point, and KASAN sees > a weird & broken mixture of LA48 and LA57 runtime semantics, right? > > Ie. as far as KASAN is concerned, the LA48 -> LA57 behavioral switchover > must be atomic, but during the kernel code patching process it isn't. Yep, half-way through the patching it observes inconsistencies and goes WTF :-)
© 2016 - 2026 Red Hat, Inc.