Le 03/12/2020 à 06:47, Alexey Kardashevskiy a écrit :
When interrupted in raw_copy_from_user()/... after user memory access
is enabled, a nested handler may also access user memory (perf is
one example) and when it does so, it calls prevent_read_from_user()
which prevents the upper handler from accessing user memory.
This saves/restores AMR when replaying interrupts.
get_kuap/set_kuap have stubs for disabled KUAP on RADIX but there are
none for hash-only configs (BOOK3E) so this adds stubs and moves
AMR_KUAP_BLOCK_xxx.
Found by syzkaller. More likely to break with enabled
CONFIG_DEBUG_ATOMIC_SLEEP, the call chain is
timer_interrupt -> ktime_get -> read_seqcount_begin -> local_irq_restore.
Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru>
---
Changes:
v2:
* fixed compile on hash
* moved get/set to arch_local_irq_restore
* block KUAP before replaying
---
This is an example:
------------[ cut here ]------------
Bug: Read fault blocked by AMR!
WARNING: CPU: 0 PID: 1603 at
/home/aik/p/kernel/arch/powerpc/include/asm/book3s/64/kup-radix.h:145
__do_page_fau
Modules linked in:
CPU: 0 PID: 1603 Comm: amr Not tainted 5.10.0-rc6_v5.10-rc6_a+fstn1 #24
NIP: c00000000009ece8 LR: c00000000009ece4 CTR: 0000000000000000
REGS: c00000000dc63560 TRAP: 0700 Not tainted (5.10.0-rc6_v5.10-rc6_a+fstn1)
MSR: 8000000000021033 <SF,ME,IR,DR,RI,LE> CR: 28002888 XER: 20040000
CFAR: c0000000001fa928 IRQMASK: 1
GPR00: c00000000009ece4 c00000000dc637f0 c000000002397600 000000000000001f
GPR04: c0000000020eb318 0000000000000000 c00000000dc63494 0000000000000027
GPR08: c00000007fe4de68 c00000000dfe9180 0000000000000000 0000000000000001
GPR12: 0000000000002000 c0000000030a0000 0000000000000000 0000000000000000
GPR16: 0000000000000000 0000000000000000 0000000000000000 bfffffffffffffff
GPR20: 0000000000000000 c0000000134a4020 c0000000019c2218 0000000000000fe0
GPR24: 0000000000000000 0000000000000000 c00000000d106200 0000000040000000
GPR28: 0000000000000000 0000000000000300 c00000000dc63910 c000000001946730
NIP [c00000000009ece8] __do_page_fault+0xb38/0xde0
LR [c00000000009ece4] __do_page_fault+0xb34/0xde0
Call Trace:
[c00000000dc637f0] [c00000000009ece4] __do_page_fault+0xb34/0xde0 (unreliable)
[c00000000dc638a0] [c00000000000c968] handle_page_fault+0x10/0x2c
--- interrupt: 300 at strncpy_from_user+0x290/0x440
LR = strncpy_from_user+0x284/0x440
[c00000000dc63ba0] [c000000000c3dcb0] strncpy_from_user+0x2f0/0x440 (unreliable)
[c00000000dc63c30] [c00000000068b888] getname_flags+0x88/0x2c0
[c00000000dc63c90] [c000000000662a44] do_sys_openat2+0x2d4/0x5f0
[c00000000dc63d30] [c00000000066560c] do_sys_open+0xcc/0x140
[c00000000dc63dc0] [c000000000045e10] system_call_exception+0x160/0x240
[c00000000dc63e20] [c00000000000da60] system_call_common+0xf0/0x27c
Instruction dump:
409c0048 3fe2ff5b 3bfff128 fac10060 fae10068 482f7a85 60000000 3c62ff5b
7fe4fb78 3863f250 4815bbd9 60000000 <0fe00000> 3c62ff5b 3863f2b8 4815c8b5
irq event stamp: 254
hardirqs last enabled at (253): [<c000000000019550>]
arch_local_irq_restore+0xa0/0x150
hardirqs last disabled at (254): [<c000000000008a10>]
data_access_common_virt+0x1b0/0x1d0
softirqs last enabled at (0): [<c0000000001f6d5c>] copy_process+0x78c/0x2120
softirqs last disabled at (0): [<0000000000000000>] 0x0
---[ end trace ba98aec5151f3aeb ]---
---
arch/powerpc/include/asm/book3s/64/kup-radix.h | 3 ---
arch/powerpc/include/asm/kup.h | 10 ++++++++++
arch/powerpc/kernel/irq.c | 6 ++++++
3 files changed, 16 insertions(+), 3 deletions(-)
diff --git a/arch/powerpc/include/asm/book3s/64/kup-radix.h
b/arch/powerpc/include/asm/book3s/64/kup-radix.h
index a39e2d193fdc..4ad607461b75 100644
--- a/arch/powerpc/include/asm/book3s/64/kup-radix.h
+++ b/arch/powerpc/include/asm/book3s/64/kup-radix.h
@@ -5,9 +5,6 @@
#include <linux/const.h>
#include <asm/reg.h>
-#define AMR_KUAP_BLOCK_READ UL(0x4000000000000000)
-#define AMR_KUAP_BLOCK_WRITE UL(0x8000000000000000)
-#define AMR_KUAP_BLOCKED (AMR_KUAP_BLOCK_READ | AMR_KUAP_BLOCK_WRITE)
#define AMR_KUAP_SHIFT 62
#ifdef __ASSEMBLY__
diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h
index 0d93331d0fab..e63930767a96 100644
--- a/arch/powerpc/include/asm/kup.h
+++ b/arch/powerpc/include/asm/kup.h
@@ -14,6 +14,10 @@
#define KUAP_CURRENT_WRITE 8
#define KUAP_CURRENT (KUAP_CURRENT_READ | KUAP_CURRENT_WRITE)
+#define AMR_KUAP_BLOCK_READ UL(0x4000000000000000)
+#define AMR_KUAP_BLOCK_WRITE UL(0x8000000000000000)
+#define AMR_KUAP_BLOCKED (AMR_KUAP_BLOCK_READ | AMR_KUAP_BLOCK_WRITE)
+
Those macro are specific to BOOK3S_64, they have nothing to do in asm/kup.h, must stay in the file
included just below
#ifdef CONFIG_PPC_BOOK3S_64
#include <asm/book3s/64/kup-radix.h>
#endif
@@ -64,6 +68,12 @@ bad_kuap_fault(struct pt_regs *regs, unsigned long address,
bool is_write)
}
static inline void kuap_check_amr(void) { }
+static inline unsigned long get_kuap(void)
+{
+ return AMR_KUAP_BLOCKED;
+}
+
The above is not generic, it is specific to book3s 64, AMR doesn't exist on
book3s/32 or on 8xx.
+static inline void set_kuap(unsigned long value) { }
/*
* book3s/64/kup-radix.h defines these functions for the !KUAP case to flush
diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index 7d0f7682d01d..d9fd46da04d6 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -314,6 +314,7 @@ void replay_soft_interrupts(void)
notrace void arch_local_irq_restore(unsigned long mask)
{
unsigned char irq_happened;
+ unsigned long kuap_state;
/* Write the new soft-enabled value */
irq_soft_mask_set(mask);
@@ -373,9 +374,14 @@ notrace void arch_local_irq_restore(unsigned long mask)
irq_soft_mask_set(IRQS_ALL_DISABLED);
trace_hardirqs_off();
+ kuap_state = get_kuap();
+ set_kuap(AMR_KUAP_BLOCKED);
+
replay_soft_interrupts();
local_paca->irq_happened = 0;
+ set_kuap(kuap_state);
+
trace_hardirqs_on();
irq_soft_mask_set(IRQS_ENABLED);
__hard_irq_enable();
