[PATCH 6.9 363/374] riscv: prevent pt_regs corruption for secondary idle threads

Greg Kroah-Hartman
2024-06-06T14:11:32Z

From: Sergey Matyukevich <sergey.matyukevich@syntacore.com>

[ Upstream commit a638b0461b58aa3205cd9d5f14d6f703d795b4af ]

Top of the kernel thread stack should be reserved for pt_regs. However
this is not the case for the idle threads of the secondary boot harts.
Their stacks overlap with their pt_regs, so both may get corrupted.

Similar issue has been fixed for the primary hart, see c7cdd96eca28
("riscv: prevent stack corruption by reserving task_pt_regs(p) early").
However that fix was not propagated to the secondary harts. The problem
has been noticed in some CPU hotplug tests with V enabled. The function
smp_callin stored several registers on stack, corrupting top of pt_regs
structure including status field. As a result, kernel attempted to save
or restore inexistent V context.

Fixes: 9a2451f18663 ("RISC-V: Avoid using per cpu array for ordered booting")
Fixes: 2875fe056156 ("RISC-V: Add cpu_ops and modify default booting method")
Signed-off-by: Sergey Matyukevich <sergey.matyukevich@syntacore.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20240523084327.2013211-1-geomatsi@gmail.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/riscv/kernel/cpu_ops_sbi.c | 2 +-
arch/riscv/kernel/cpu_ops_spinwait.c | 3 +--
2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/kernel/cpu_ops_sbi.c b/arch/riscv/kernel/cpu_ops_sbi.c
index 1cc7df740eddc..e6fbaaf549562 100644
--- a/arch/riscv/kernel/cpu_ops_sbi.c
+++ b/arch/riscv/kernel/cpu_ops_sbi.c
@@ -72,7 +72,7 @@ static int sbi_cpu_start(unsigned int cpuid, struct task_struct *tidle)
/* Make sure tidle is updated */
smp_mb();
bdata->task_ptr = tidle;
- bdata->stack_ptr = task_stack_page(tidle) + THREAD_SIZE;
+ bdata->stack_ptr = task_pt_regs(tidle);
/* Make sure boot data is updated */
smp_mb();
hsm_data = __pa(bdata);
diff --git a/arch/riscv/kernel/cpu_ops_spinwait.c b/arch/riscv/kernel/cpu_ops_spinwait.c
index 613872b0a21ac..24869eb889085 100644
--- a/arch/riscv/kernel/cpu_ops_spinwait.c
+++ b/arch/riscv/kernel/cpu_ops_spinwait.c
@@ -34,8 +34,7 @@ static void cpu_update_secondary_bootdata(unsigned int cpuid,

/* Make sure tidle is updated */
smp_mb();
- WRITE_ONCE(__cpu_spinwait_stack_pointer[hartid],
- task_stack_page(tidle) + THREAD_SIZE);
+ WRITE_ONCE(__cpu_spinwait_stack_pointer[hartid], task_pt_regs(tidle));
WRITE_ONCE(__cpu_spinwait_task_pointer[hartid], tidle);
}

--
2.43.0