Subject: Re: [PATCH v2 29/37] powerpc/nohash: Replace pte_user() by pte_read()

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Tue, 07 Nov 2023 19:04:22 +0530

Christophe Leroy <[email-masked]> writes:

> Le 31/10/2023 à 11:15, Aneesh Kumar K.V a écrit :
>> Christophe Leroy <[email-masked]> writes:
>> 
>>> pte_user() is now only used in pte_access_permitted() to check
>>> access on vmas. User flag is cleared to make a page unreadable.
>>>
>>> So rename it pte_read() and remove pte_user() which isn't used
>>> anymore.
>>>
>>> For the time being it checks _PAGE_USER but in the near futur
>>> all plateforms will be converted to _PAGE_READ so lets support
>>> both for now.
>>>
>>> Signed-off-by: Christophe Leroy <[email-masked]>
>>> ---
>>>   arch/powerpc/include/asm/nohash/32/pte-8xx.h |  7 -------
>>>   arch/powerpc/include/asm/nohash/pgtable.h    | 13 +++++++------
>>>   arch/powerpc/mm/ioremap.c                    |  4 ----
>>>   3 files changed, 7 insertions(+), 17 deletions(-)
>>>
>>> diff --git a/arch/powerpc/include/asm/nohash/32/pte-8xx.h b/arch/powerpc/include/asm/nohash/32/pte-8xx.h
>>> index 62c965a4511a..1ee38befd29a 100644
>>> --- a/arch/powerpc/include/asm/nohash/32/pte-8xx.h
>>> +++ b/arch/powerpc/include/asm/nohash/32/pte-8xx.h
>>> @@ -112,13 +112,6 @@ static inline pte_t pte_mkwrite_novma(pte_t pte)
>>>   
>>>   #define pte_mkwrite_novma pte_mkwrite_novma
>>>   
>>> -static inline bool pte_user(pte_t pte)
>>> -{
>>> -	return !(pte_val(pte) & _PAGE_SH);
>>> -}
>>> -
>>> -#define pte_user pte_user
>>> -
>>>   static inline pte_t pte_mkhuge(pte_t pte)
>>>   {
>>>   	return __pte(pte_val(pte) | _PAGE_SPS | _PAGE_HUGE);
>>> diff --git a/arch/powerpc/include/asm/nohash/pgtable.h b/arch/powerpc/include/asm/nohash/pgtable.h
>>> index ee677162f9e6..aba56fe3b1c6 100644
>>> --- a/arch/powerpc/include/asm/nohash/pgtable.h
>>> +++ b/arch/powerpc/include/asm/nohash/pgtable.h
>>> @@ -160,9 +160,6 @@ static inline int pte_write(pte_t pte)
>>>   	return pte_val(pte) & _PAGE_WRITE;
>>>   }
>>>   #endif
>>> -#ifndef pte_read
>>> -static inline int pte_read(pte_t pte)		{ return 1; }
>>> -#endif
>>>   static inline int pte_dirty(pte_t pte)		{ return pte_val(pte) & _PAGE_DIRTY; }
>>>   static inline int pte_special(pte_t pte)	{ return pte_val(pte) & _PAGE_SPECIAL; }
>>>   static inline int pte_none(pte_t pte)		{ return (pte_val(pte) & ~_PTE_NONE_MASK) == 0; }
>>> @@ -190,10 +187,14 @@ static inline int pte_young(pte_t pte)
>>>    * and PTE_64BIT, PAGE_KERNEL_X contains _PAGE_BAP_SR which is also in
>>>    * _PAGE_USER.  Need to explicitly match _PAGE_BAP_UR bit in that case too.
>>>    */
>>> -#ifndef pte_user
>>> -static inline bool pte_user(pte_t pte)
>>> +#ifndef pte_read
>>> +static inline bool pte_read(pte_t pte)
>>>   {
>>> +#ifdef _PAGE_READ
>>> +	return (pte_val(pte) & _PAGE_READ) == _PAGE_READ;
>>> +#else
>>>   	return (pte_val(pte) & _PAGE_USER) == _PAGE_USER;
>>> +#endif
>>>   }
>>>   #endif
>>>   
>>> @@ -208,7 +209,7 @@ static inline bool pte_access_permitted(pte_t pte, bool write)
>>>   	 * A read-only access is controlled by _PAGE_USER bit.
>>>   	 * We have _PAGE_READ set for WRITE and EXECUTE
>>>   	 */
>>> -	if (!pte_present(pte) || !pte_user(pte) || !pte_read(pte))
>>> +	if (!pte_present(pte) || !pte_read(pte))
>>>   		return false;
>>>   
>>>   	if (write && !pte_write(pte))
>>> diff --git a/arch/powerpc/mm/ioremap.c b/arch/powerpc/mm/ioremap.c
>>> index 7823c38f09de..7b0afcabd89f 100644
>>> --- a/arch/powerpc/mm/ioremap.c
>>> +++ b/arch/powerpc/mm/ioremap.c
>>> @@ -50,10 +50,6 @@ void __iomem *ioremap_prot(phys_addr_t addr, size_t size, unsigned long flags)
>>>   	if (pte_write(pte))
>>>   		pte = pte_mkdirty(pte);
>>>   
>>> -	/* we don't want to let _PAGE_USER leak out */
>>> -	if (WARN_ON(pte_user(pte)))
>>> -		return NULL;
>>>
>> 
>> This check is still valid right? I understand that we want to remove
>> _PAGE_USER. But then loosing this check is ok?
>
> Well, we may have to think about it for book3s/64. For all others 
> _PAGE_USER is gone and replaced by a check of addresses versus TASK_SIZE.
>
> As ioremap() will map into vmalloc space that address is necesserally 
> correct.
> 
>

We are adding the pte flags check not the map addr check there. Something like this?

diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index 7c7de7b56df0..b053b86e0069 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
@@ -1462,5 +1462,11 @@ static inline bool pud_is_leaf(pud_t pud)
 	return !!(pud_raw(pud) & cpu_to_be64(_PAGE_PTE));
 }
 
+#define arch_ioremap_valid_pte arch_ioremap_valid_pte
+static inline bool arch_ioremap_valid_pte(pte_t pte)
+{
+	return !!(pte_raw(pte) & cpu_to_be64(_PAGE_PRIVILEGED));
+}
+
 #endif /* __ASSEMBLY__ */
 #endif /* _ASM_POWERPC_BOOK3S_64_PGTABLE_H_ */
diff --git a/arch/powerpc/include/asm/nohash/32/pte-8xx.h b/arch/powerpc/include/asm/nohash/32/pte-8xx.h
index 137dc3c84e45..7b23d2543528 100644
--- a/arch/powerpc/include/asm/nohash/32/pte-8xx.h
+++ b/arch/powerpc/include/asm/nohash/32/pte-8xx.h
@@ -223,5 +223,11 @@ static inline pte_t ptep_get(pte_t *ptep)
 
 #endif
 
+#define arch_ioremap_valid_pte arch_ioremap_valid_pte
+static inline bool arch_ioremap_valid_pte(pte_t pte)
+{
+	return !!(pte_val(pte) & (_PAGE_SH))
+}
+
 #endif /* __KERNEL__ */
 #endif /*  _ASM_POWERPC_NOHASH_32_PTE_8xx_H */
diff --git a/arch/powerpc/include/asm/nohash/pte-e500.h b/arch/powerpc/include/asm/nohash/pte-e500.h
index f516f0b5b7a8..d31274178aa6 100644
--- a/arch/powerpc/include/asm/nohash/pte-e500.h
+++ b/arch/powerpc/include/asm/nohash/pte-e500.h
@@ -105,6 +105,13 @@ static inline pte_t pte_mkexec(pte_t pte)
 }
 #define pte_mkexec pte_mkexec
 
+#define arch_ioremap_valid_pte arch_ioremap_valid_pte
+static inline bool arch_ioremap_valid_pte(pte_t pte)
+{
+	return !(pte_val(pte) & (_PAGE_BAP_UR | _PAGE_BAP_UW | _PAGE_BAP_UX))
+}
+
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __KERNEL__ */
diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
index 2bfb7dd3b49e..417abe5dcbd8 100644
--- a/arch/powerpc/include/asm/pgtable.h
+++ b/arch/powerpc/include/asm/pgtable.h
@@ -231,6 +231,13 @@ static inline bool arch_supports_memmap_on_memory(unsigned long vmemmap_size)
 
 #endif /* CONFIG_PPC64 */
 
+#ifndef arch_ioremap_valid_pte
+static inline book arch_ioremap_valid_pte(pte_t pte)
+{
+	return true;
+}
+#endif
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_POWERPC_PGTABLE_H */
diff --git a/arch/powerpc/mm/ioremap.c b/arch/powerpc/mm/ioremap.c
index 7b0afcabd89f..1a39e698c3d4 100644
--- a/arch/powerpc/mm/ioremap.c
+++ b/arch/powerpc/mm/ioremap.c
@@ -50,6 +50,9 @@ void __iomem *ioremap_prot(phys_addr_t addr, size_t size, unsigned long flags)
 	if (pte_write(pte))
 		pte = pte_mkdirty(pte);
 
+	if (WARN_ON(!arch_ioremap_valid_pte(pte)))
+		return NULL;
+
 	if (iowa_is_active())
 		return iowa_ioremap(addr, size, pte_pgprot(pte), caller);
 	return __ioremap_caller(addr, size, pte_pgprot(pte), caller);