[PATCH] x86/alternatives: Disable KASAN on text_poke_early() in apply_alternatives()

Kirill A. Shutemov
2023-10-10T05:37:38Z

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().

It seems that 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.

During text_poke_early() in apply_alternatives(), KASAN should be
disabled. KASAN is already disabled in non-_early() text_poke().

It is unclear why the issue was not reported earlier. Bisecting does not
help. Older kernels trigger the issue less frequently, but it still
occurs. In the absence of any other clear offenders, the initial dynamic
5-level paging support is to blame.

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
---
arch/x86/kernel/alternative.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 517ee01503be..56187fd8816e 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -450,7 +450,9 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
DUMP_BYTES(ALT, replacement, a->replacementlen, "%px: rpl_insn: ", replacement);
DUMP_BYTES(ALT, insn_buff, insn_buff_sz, "%px: final_insn: ", instr);

+ kasan_disable_current();
text_poke_early(instr, insn_buff, insn_buff_sz);
+ kasan_enable_current();
}
}

--
2.41.0