[PATCH] RISC-V: prevent sbi_send_cpumask_ipi race with ftrace

[Dimitri John Ledkov]

From: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx>

ftrace will patch instructions in sbi_send_cpumask_ipi, which is going to
be used by flush_icache_range, leading to potential races and crashes like
this:

[    0.000000] ftrace: allocating 38893 entries in 152 pages
[    0.000000] Oops - illegal instruction [#1]
[    0.000000] Modules linked in:
[    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 5.11.0-1014-generic #14-Ubuntu
[    0.000000] epc: ffffffe00000920e ra : ffffffe000009384 sp : ffffffe001803d30
[    0.000000]  gp : ffffffe001a14240 tp : ffffffe00180f440 t0 : ffffffe07fe38000
[    0.000000]  t1 : ffffffe0019cd338 t2 : 0000000000000000 s0 : ffffffe001803d70
[    0.000000]  s1 : 0000000000000000 a0 : ffffffe0000095aa a1 : 0000000000000001
[    0.000000]  a2 : 0000000000000002 a3 : 0000000000000000 a4 : 0000000000000000
[    0.000000]  a5 : 0000000000000000 a6 : 0000000000000004 a7 : 0000000052464e43
[    0.000000]  s2 : 0000000000000002 s3 : 0000000000000001 s4 : 0000000000000000
[    0.000000]  s5 : 0000000000000000 s6 : 0000000000000000 s7 : 0000000000000000
[    0.000000]  s8 : ffffffe001a170c0 s9 : 0000000000000001 s10: 0000000000000001
[    0.000000]  s11: 00000000fffcc5d0 t3 : 0000000000000068 t4 : 000000000000000b
[    0.000000]  t5 : ffffffe0019cd3e0 t6 : ffffffe001803cd8
[    0.000000] status: 0000000200000100 badaddr: 000000000513f187 cause: 0000000000000002
[    0.000000] ---[ end trace f67eb9af4d8d492b ]---
[    0.000000] Kernel panic - not syncing: Attempted to kill the idle task!
[    0.000000] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---

Where ffffffe00000920e lies in the middle of sbi_send_cpumask_ipi.

Reproduced on Unmatched board using Ubuntu kernels. See
https://people.canonical.com/~xnox/lp1934548/ for sample images,
kernels, debug symbols.

BugLink: https://bugs.launchpad.net/bugs/1934548
Reported-by: Pierce Andjelkovic <pierceandjelkovic@xxxxxxxxx>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx>
Signed-off-by: Dimitri John Ledkov <dimitri.ledkov@xxxxxxxxxxxxx>
cc: Paul Walmsley <paul.walmsley@xxxxxxxxxx>
cc: linux-riscv@xxxxxxxxxxxxxxxxxxx
cc: stable@xxxxxxxxxxxxxxx
---
 arch/riscv/kernel/sbi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
index 7402a417f38e..158199865c68 100644
--- a/arch/riscv/kernel/sbi.c
+++ b/arch/riscv/kernel/sbi.c
@@ -562,7 +562,7 @@ long sbi_get_mimpid(void)
 	return __sbi_base_ecall(SBI_EXT_BASE_GET_MIMPID);
 }
 
-static void sbi_send_cpumask_ipi(const struct cpumask *target)
+static void notrace sbi_send_cpumask_ipi(const struct cpumask *target)
 {
 	struct cpumask hartid_mask;
 
-- 
2.30.2