[PATCH] powerpc/64: poison __per_cpu_offset to catch use-before-init
DORMANTno replies
From: Nicholas Piggin <npiggin@gmail.com>
Date: 2022-10-06 14:49:25
Subsystem:
linux for powerpc (32-bit and 64-bit), per-cpu memory allocator, the rest · Maintainers:
Madhavan Srinivasan, Dennis Zhou, Tejun Heo, Christoph Lameter, Linus Torvalds
If the boot CPU tries to access per-cpu data of other CPUs before per cpu areas are set up, it will unexpectedly use offset 0. Try to catch such accesses by poisoning the __per_cpu_offset array. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> --- With the early boot machine check handler added to 64s, this might be worth another try. We did have a bug in mce_init() that was using cpu_to_node() too early that would be caught by this. Thanks, Nick arch/powerpc/include/asm/percpu.h | 1 + arch/powerpc/kernel/paca.c | 2 +- arch/powerpc/kernel/setup_64.c | 3 ++- 3 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/include/asm/percpu.h b/arch/powerpc/include/asm/percpu.h
index 8e5b7d0b851c..6ca1a9fc5725 100644
--- a/arch/powerpc/include/asm/percpu.h
+++ b/arch/powerpc/include/asm/percpu.h@@ -7,6 +7,7 @@ * Same as asm-generic/percpu.h, except that we store the per cpu offset * in the paca. Based on the x86-64 implementation. */ +#define PER_CPU_OFFSET_POISON 0xfeeeeeeeeeeeeeeeULL #ifdef CONFIG_SMP
diff --git a/arch/powerpc/kernel/paca.c b/arch/powerpc/kernel/paca.c
index be8db402e963..c33de70596e7 100644
--- a/arch/powerpc/kernel/paca.c
+++ b/arch/powerpc/kernel/paca.c@@ -198,7 +198,7 @@ void __init initialise_paca(struct paca_struct *new_paca, int cpu) new_paca->hw_cpu_id = 0xffff; new_paca->kexec_state = KEXEC_STATE_NONE; new_paca->__current = &init_task; - new_paca->data_offset = 0xfeeeeeeeeeeeeeeeULL; + new_paca->data_offset = PER_CPU_OFFSET_POISON; #ifdef CONFIG_PPC_64S_HASH_MMU new_paca->slb_shadow_ptr = NULL; #endif
diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index a0dee7354fe6..039a4eac03c3 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c@@ -362,6 +362,7 @@ void __init early_setup(unsigned long dt_ptr) * So set up a temporary paca. It will be replaced below once we know * what CPU we are on. */ + __per_cpu_offset[0] = 0; initialise_paca(&boot_paca, 0); fixup_boot_paca(&boot_paca); WARN_ON(local_paca != 0);
@@ -828,7 +829,7 @@ static __init int pcpu_cpu_to_node(int cpu) return early_cpu_to_node(cpu); } -unsigned long __per_cpu_offset[NR_CPUS] __read_mostly; +unsigned long __per_cpu_offset[NR_CPUS] __read_mostly = { [0 ... NR_CPUS-1 ] = PER_CPU_OFFSET_POISON }; EXPORT_SYMBOL(__per_cpu_offset); void __init setup_per_cpu_areas(void)
--
2.37.2