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)
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?
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.
* 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 triggersbecause 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 triggersbecause 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 :-)
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 triggersbecause 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.
* 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
linux-stable-mirror@lists.linaro.org
-
Ingo Molnar -
Kirill A. Shutemov -
Peter Zijlstra