[PATCH v2] arm64: mm: Fix CFI failure due to kpti_ng_pgd_alloc function signature

[PATCH v2] arm64: mm: Fix CFI failure due to kpti_ng_pgd_alloc function signature

[Kees Cook]

Seen during KPTI initialization:

  CFI failure at create_kpti_ng_temp_pgd+0x124/0xce8 (target: kpti_ng_pgd_alloc+0x0/0x14; expected type: 0xd61b88b6)

The call site is alloc_init_pud() at arch/arm64/mm/mmu.c:

  pud_phys = pgtable_alloc(TABLE_PUD);

alloc_init_pud() has the prototype:

  static void alloc_init_pud(p4d_t *p4dp, unsigned long addr, unsigned long end,
                             phys_addr_t phys, pgprot_t prot,
                             phys_addr_t (*pgtable_alloc)(enum pgtable_type),
                             int flags)

where the pgtable_alloc() prototype is declared.

The target (kpti_ng_pgd_alloc) is used in arch/arm64/kernel/cpufeature.c:

  create_kpti_ng_temp_pgd(kpti_ng_temp_pgd, __pa(alloc), KPTI_NG_TEMP_VA,
                          PAGE_SIZE, PAGE_KERNEL, kpti_ng_pgd_alloc, 0);

which is an alias for __create_pgd_mapping_locked() with prototype:

  extern __alias(__create_pgd_mapping_locked)
  void create_kpti_ng_temp_pgd(pgd_t *pgdir, phys_addr_t phys,
                               unsigned long virt,
                               phys_addr_t size, pgprot_t prot,
                               phys_addr_t (*pgtable_alloc)(enum pgtable_type),
                               int flags);

__create_pgd_mapping_locked() passes the function pointer down:

  __create_pgd_mapping_locked() -> alloc_init_p4d() -> alloc_init_pud()

But the target function (kpti_ng_pgd_alloc) has the wrong signature:

  static phys_addr_t __init kpti_ng_pgd_alloc(int shift);

The "int" should be "enum pgtable_type".

To make "enum pgtable_type" available to cpufeature.c, move
enum pgtable_type definition from arch/arm64/mm/mmu.c to
arch/arm64/include/asm/mmu.h.

Adjust kpti_ng_pgd_alloc to use "enum pgtable_type" instead of "int".
The function behavior remains identical (parameter is unused).

Fixes: c64f46ee1377 ("arm64: mm: use enum to identify pgtable level instead of *_SHIFT")
Signed-off-by: Kees Cook <kees@kernel.org>
---
 v2: Fixed the Fixes line. ;)
 v1: https://lore.kernel.org/lkml/20250829154913.work.943-kees@kernel.org/
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Oliver Upton <oliver.upton@linux.dev>
Cc: Yue Haibing <yuehaibing@huawei.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: <linux-arm-kernel@lists.infradead.org>
---
 arch/arm64/include/asm/mmu.h   | 7 +++++++
 arch/arm64/kernel/cpufeature.c | 5 +++--
 arch/arm64/mm/mmu.c            | 7 -------
 3 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
index 6e8aa8e72601..49f1a810df16 100644
--- a/arch/arm64/include/asm/mmu.h
+++ b/arch/arm64/include/asm/mmu.h
@@ -17,6 +17,13 @@
 #include <linux/refcount.h>
 #include <asm/cpufeature.h>
 
+enum pgtable_type {
+	TABLE_PTE,
+	TABLE_PMD,
+	TABLE_PUD,
+	TABLE_P4D,
+};
+
 typedef struct {
 	atomic64_t	id;
 #ifdef CONFIG_COMPAT
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 9ad065f15f1d..e49d142a281f 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -84,6 +84,7 @@
 #include <asm/hwcap.h>
 #include <asm/insn.h>
 #include <asm/kvm_host.h>
+#include <asm/mmu.h>
 #include <asm/mmu_context.h>
 #include <asm/mte.h>
 #include <asm/hypervisor.h>
@@ -1945,11 +1946,11 @@ static bool has_pmuv3(const struct arm64_cpu_capabilities *entry, int scope)
 extern
 void create_kpti_ng_temp_pgd(pgd_t *pgdir, phys_addr_t phys, unsigned long virt,
 			     phys_addr_t size, pgprot_t prot,
-			     phys_addr_t (*pgtable_alloc)(int), int flags);
+			     phys_addr_t (*pgtable_alloc)(enum pgtable_type), int flags);
 
 static phys_addr_t __initdata kpti_ng_temp_alloc;
 
-static phys_addr_t __init kpti_ng_pgd_alloc(int shift)
+static phys_addr_t __init kpti_ng_pgd_alloc(enum pgtable_type type)
 {
 	kpti_ng_temp_alloc -= PAGE_SIZE;
 	return kpti_ng_temp_alloc;
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 34e5d78af076..183801520740 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -47,13 +47,6 @@
 #define NO_CONT_MAPPINGS	BIT(1)
 #define NO_EXEC_MAPPINGS	BIT(2)	/* assumes FEAT_HPDS is not used */
 
-enum pgtable_type {
-	TABLE_PTE,
-	TABLE_PMD,
-	TABLE_PUD,
-	TABLE_P4D,
-};
-
 u64 kimage_voffset __ro_after_init;
 EXPORT_SYMBOL(kimage_voffset);
 
-- 
2.34.1

Re: [PATCH v2] arm64: mm: Fix CFI failure due to kpti_ng_pgd_alloc function signature

[David Hildenbrand]

On 29.08.25 21:07, Kees Cook wrote:
> Seen during KPTI initialization:
> 
>    CFI failure at create_kpti_ng_temp_pgd+0x124/0xce8 (target: kpti_ng_pgd_alloc+0x0/0x14; expected type: 0xd61b88b6)
> 
> The call site is alloc_init_pud() at arch/arm64/mm/mmu.c:
> 
>    pud_phys = pgtable_alloc(TABLE_PUD);
> 
> alloc_init_pud() has the prototype:
> 
>    static void alloc_init_pud(p4d_t *p4dp, unsigned long addr, unsigned long end,
>                               phys_addr_t phys, pgprot_t prot,
>                               phys_addr_t (*pgtable_alloc)(enum pgtable_type),
>                               int flags)
> 
> where the pgtable_alloc() prototype is declared.
> 
> The target (kpti_ng_pgd_alloc) is used in arch/arm64/kernel/cpufeature.c:
> 
>    create_kpti_ng_temp_pgd(kpti_ng_temp_pgd, __pa(alloc), KPTI_NG_TEMP_VA,
>                            PAGE_SIZE, PAGE_KERNEL, kpti_ng_pgd_alloc, 0);
> 
> which is an alias for __create_pgd_mapping_locked() with prototype:
> 
>    extern __alias(__create_pgd_mapping_locked)
>    void create_kpti_ng_temp_pgd(pgd_t *pgdir, phys_addr_t phys,
>                                 unsigned long virt,
>                                 phys_addr_t size, pgprot_t prot,
>                                 phys_addr_t (*pgtable_alloc)(enum pgtable_type),
>                                 int flags);
> 
> __create_pgd_mapping_locked() passes the function pointer down:
> 
>    __create_pgd_mapping_locked() -> alloc_init_p4d() -> alloc_init_pud()
> 
> But the target function (kpti_ng_pgd_alloc) has the wrong signature:
> 
>    static phys_addr_t __init kpti_ng_pgd_alloc(int shift);
> 
> The "int" should be "enum pgtable_type".
> 
> To make "enum pgtable_type" available to cpufeature.c, move
> enum pgtable_type definition from arch/arm64/mm/mmu.c to
> arch/arm64/include/asm/mmu.h.
> 
> Adjust kpti_ng_pgd_alloc to use "enum pgtable_type" instead of "int".
> The function behavior remains identical (parameter is unused).
> 
> Fixes: c64f46ee1377 ("arm64: mm: use enum to identify pgtable level instead of *_SHIFT")
> Signed-off-by: Kees Cook <kees@kernel.org>
> ---
>   v2: Fixed the Fixes line. ;)
>   v1: https://lore.kernel.org/lkml/20250829154913.work.943-kees@kernel.org/
> Cc: Kevin Brodsky <kevin.brodsky@arm.com>
> Cc: Ard Biesheuvel <ardb@kernel.org>
> Cc: Ryan Roberts <ryan.roberts@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> Cc: Oliver Upton <oliver.upton@linux.dev>
> Cc: Yue Haibing <yuehaibing@huawei.com>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: <linux-arm-kernel@lists.infradead.org>
> ---
>   arch/arm64/include/asm/mmu.h   | 7 +++++++
>   arch/arm64/kernel/cpufeature.c | 5 +++--
>   arch/arm64/mm/mmu.c            | 7 -------
>   3 files changed, 10 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
> index 6e8aa8e72601..49f1a810df16 100644
> --- a/arch/arm64/include/asm/mmu.h
> +++ b/arch/arm64/include/asm/mmu.h
> @@ -17,6 +17,13 @@
>   #include <linux/refcount.h>
>   #include <asm/cpufeature.h>
>   
> +enum pgtable_type {
> +	TABLE_PTE,
> +	TABLE_PMD,
> +	TABLE_PUD,
> +	TABLE_P4D,
> +};

Just noting that we now have "enum pgtable_level" in 
include/linux/pgtable.h that could at some point possibly be used here 
instead (not in this fix).

-- 
Cheers

David / dhildenb

Re: [PATCH v2] arm64: mm: Fix CFI failure due to kpti_ng_pgd_alloc function signature

[Kevin Brodsky]

On 29/08/2025 21:13, David Hildenbrand wrote:
>> [...]
>>
>> diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
>> index 6e8aa8e72601..49f1a810df16 100644
>> --- a/arch/arm64/include/asm/mmu.h
>> +++ b/arch/arm64/include/asm/mmu.h
>> @@ -17,6 +17,13 @@
>>   #include <linux/refcount.h>
>>   #include <asm/cpufeature.h>
>>   +enum pgtable_type {
>> +    TABLE_PTE, m68k_table_types
>> +    TABLE_PMD,
>> +    TABLE_PUD,
>> +    TABLE_P4D,
>> +};
>
> Just noting that we now have "enum pgtable_level" in
> include/linux/pgtable.h that could at some point possibly be used here
> instead (not in this fix). 

Thanks for the heads-up! I'll look into using the new generic enum
instead, there's really no need for every architecture to invent its
own. m68k could also use it instead of m68k_table_types.

- Kevin

Re: [PATCH v2] arm64: mm: Fix CFI failure due to kpti_ng_pgd_alloc function signature

[Catalin Marinas]

On Fri, 29 Aug 2025 12:07:25 -0700, Kees Cook wrote:
> Seen during KPTI initialization:
> 
>   CFI failure at create_kpti_ng_temp_pgd+0x124/0xce8 (target: kpti_ng_pgd_alloc+0x0/0x14; expected type: 0xd61b88b6)
> 
> The call site is alloc_init_pud() at arch/arm64/mm/mmu.c:
> 
>   pud_phys = pgtable_alloc(TABLE_PUD);
> 
> [...]

Applied to arm64 (for-next/fixes), thanks!

[1/1] arm64: mm: Fix CFI failure due to kpti_ng_pgd_alloc function signature
      https://git.kernel.org/arm64/c/ceca927c86e6

I added the acks from v1 directly as there's no change.

-- 
Catalin