From: Mahesh Salgaonkar mahesh@linux.ibm.com

[ Upstream commit 0db880fc865ffb522141ced4bfa66c12ab1fbb70 ]

nmi_enter()/nmi_exit() touches per cpu variables which can lead to kernel crash when invoked during real mode interrupt handling (e.g. early HMI/MCE interrupt handler) if percpu allocation comes from vmalloc area.

Early HMI/MCE handlers are called through DEFINE_INTERRUPT_HANDLER_NMI() wrapper which invokes nmi_enter/nmi_exit calls. We don't see any issue when percpu allocation is from the embedded first chunk. However with CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK enabled there are chances where percpu allocation can come from the vmalloc area.

With kernel command line "percpu_alloc=page" we can force percpu allocation to come from vmalloc area and can see kernel crash in machine_check_early:

[ 1.215714] NIP [c000000000e49eb4] rcu_nmi_enter+0x24/0x110 [ 1.215717] LR [c0000000000461a0] machine_check_early+0xf0/0x2c0 [ 1.215719] --- interrupt: 200 [ 1.215720] [c000000fffd73180] [0000000000000000] 0x0 (unreliable) [ 1.215722] [c000000fffd731b0] [0000000000000000] 0x0 [ 1.215724] [c000000fffd73210] [c000000000008364] machine_check_early_common+0x134/0x1f8

Fix this by avoiding use of nmi_enter()/nmi_exit() in real mode if percpu first chunk is not embedded.

CVE-2024-42126 Cc: stable@vger.kernel.org#5.15.x Cc: gregkh@linuxfoundation.org Reviewed-by: Christophe Leroy christophe.leroy@csgroup.eu Tested-by: Shirisha Ganta shirisha@linux.ibm.com Signed-off-by: Mahesh Salgaonkar mahesh@linux.ibm.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://msgid.link/20240410043006.81577-1-mahesh@linux.ibm.com [ Conflicts in arch/powerpc/include/asm/interrupt.h because interrupt_nmi_enter_prepare() and interrupt_nmi_exit_prepare() has been refactored. ] Signed-off-by: Jinjie Ruan ruanjinjie@huawei.com --- arch/powerpc/include/asm/interrupt.h | 14 ++++++++++---- arch/powerpc/include/asm/percpu.h | 10 ++++++++++ arch/powerpc/kernel/setup_64.c | 2 ++ 3 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/include/asm/interrupt.h b/arch/powerpc/include/asm/interrupt.h index e592e65e7665..49285b147afe 100644 --- a/arch/powerpc/include/asm/interrupt.h +++ b/arch/powerpc/include/asm/interrupt.h @@ -285,18 +285,24 @@ static inline void interrupt_nmi_enter_prepare(struct pt_regs *regs, struct inte /* * Do not use nmi_enter() for pseries hash guest taking a real-mode * NMI because not everything it touches is within the RMA limit. + * + * Likewise, do not use it in real mode if percpu first chunk is not + * embedded. With CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK enabled there + * are chances where percpu allocation can come from vmalloc area. */ - if (!IS_ENABLED(CONFIG_PPC_BOOK3S_64) || + if ((!IS_ENABLED(CONFIG_PPC_BOOK3S_64) || !firmware_has_feature(FW_FEATURE_LPAR) || - radix_enabled() || (mfmsr() & MSR_DR)) + radix_enabled() || (mfmsr() & MSR_DR)) && + !percpu_first_chunk_is_paged) nmi_enter(); }

static inline void interrupt_nmi_exit_prepare(struct pt_regs *regs, struct interrupt_nmi_state *state) { - if (!IS_ENABLED(CONFIG_PPC_BOOK3S_64) || + if ((!IS_ENABLED(CONFIG_PPC_BOOK3S_64) || !firmware_has_feature(FW_FEATURE_LPAR) || - radix_enabled() || (mfmsr() & MSR_DR)) + radix_enabled() || (mfmsr() & MSR_DR)) && + !percpu_first_chunk_is_paged) nmi_exit();

/* diff --git a/arch/powerpc/include/asm/percpu.h b/arch/powerpc/include/asm/percpu.h index 8e5b7d0b851c..634970ce13c6 100644 --- a/arch/powerpc/include/asm/percpu.h +++ b/arch/powerpc/include/asm/percpu.h @@ -15,6 +15,16 @@ #endif /* CONFIG_SMP */ #endif /* __powerpc64__ */

+#if defined(CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK) && defined(CONFIG_SMP) +#include <linux/jump_label.h> +DECLARE_STATIC_KEY_FALSE(__percpu_first_chunk_is_paged); + +#define percpu_first_chunk_is_paged \ + (static_key_enabled(&__percpu_first_chunk_is_paged.key)) +#else +#define percpu_first_chunk_is_paged false +#endif /* CONFIG_PPC64 && CONFIG_SMP */ + #include <asm-generic/percpu.h>

#include <asm/paca.h> diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c index eaa79a0996d1..37d5683ab298 100644 --- a/arch/powerpc/kernel/setup_64.c +++ b/arch/powerpc/kernel/setup_64.c @@ -825,6 +825,7 @@ static int pcpu_cpu_distance(unsigned int from, unsigned int to)

unsigned long __per_cpu_offset[NR_CPUS] __read_mostly; EXPORT_SYMBOL(__per_cpu_offset); +DEFINE_STATIC_KEY_FALSE(__percpu_first_chunk_is_paged);

static void __init pcpu_populate_pte(unsigned long addr) { @@ -904,6 +905,7 @@ void __init setup_per_cpu_areas(void) if (rc < 0) panic("cannot initialize percpu area (err=%d)", rc);

+ static_key_enable(&__percpu_first_chunk_is_paged.key); delta = (unsigned long)pcpu_base_addr - (unsigned long)__per_cpu_start; for_each_possible_cpu(cpu) { __per_cpu_offset[cpu] = delta + pcpu_unit_offsets[cpu];