linux-kernel - Re: [PATCH v2 02/10] powerpc/book3e: Fix set_memory_x() and set_memory

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Date:   Mon, 25 Oct 2021 23:53:41 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 02/10] powerpc/book3e: Fix set_memory_x() and
 set_memory_nx()



On 23/10/2021 13:47, Christophe Leroy wrote:
> set_memory_x() calls pte_mkexec() which sets _PAGE_EXEC.
> set_memory_nx() calls pte_exprotec() which clears _PAGE_EXEC.
> 
> Book3e has 2 bits, UX and SX, which defines the exec rights
> resp. for user (PR=1) and for kernel (PR=0).
> 
> _PAGE_EXEC is defined as UX only.
> 
> An executable kernel page is set with either _PAGE_KERNEL_RWX
> or _PAGE_KERNEL_ROX, which both have SX set and UX cleared.
> 
> So set_memory_nx() call for an executable kernel page does
> nothing because UX is already cleared.
> 
> And set_memory_x() on a non-executable kernel page makes it
> executable for the user and keeps it non-executable for kernel.
> 
> Also, pte_exec() always returns 'false' on kernel pages, because
> it checks _PAGE_EXEC which doesn't include SX, so for instance
> the W+X check doesn't work.
> 
> To fix this:
> - change tlb_low_64e.S to use _PAGE_BAP_UX instead of _PAGE_USER
> - sets both UX and SX in _PAGE_EXEC so that pte_user() returns
> true whenever one of the two bits is set and pte_exprotect()
> clears both bits.
> - Define a book3e specific version of pte_mkexec() which sets
> either SX or UX based on UR.
> 
> Fixes: 1f9ad21c3b38 ("powerpc/mm: Implement set_memory() routines")
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
> v2: New

pte_mkexec() in nohash/64/pgtable.h conflicts with the one in 
nohash/pte_book3e.h

Should guard it with  #ifndef pte_mkexec(), but as pte_book3e is the 
only user in 64 bits, then just remove it from there.

Send v3 with only that change compared to v2.

Christophe

> ---
>   arch/powerpc/include/asm/nohash/32/pgtable.h |  2 ++
>   arch/powerpc/include/asm/nohash/pte-book3e.h | 18 ++++++++++++++----
>   arch/powerpc/mm/nohash/tlb_low_64e.S         |  8 ++++----
>   3 files changed, 20 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/nohash/32/pgtable.h b/arch/powerpc/include/asm/nohash/32/pgtable.h
> index ac0a5ff48c3a..d6ba821a56ce 100644
> --- a/arch/powerpc/include/asm/nohash/32/pgtable.h
> +++ b/arch/powerpc/include/asm/nohash/32/pgtable.h
> @@ -193,10 +193,12 @@ static inline pte_t pte_wrprotect(pte_t pte)
>   }
>   #endif
>   
> +#ifndef pte_mkexec
>   static inline pte_t pte_mkexec(pte_t pte)
>   {
>   	return __pte(pte_val(pte) | _PAGE_EXEC);
>   }
> +#endif
>   
>   #define pmd_none(pmd)		(!pmd_val(pmd))
>   #define	pmd_bad(pmd)		(pmd_val(pmd) & _PMD_BAD)
> diff --git a/arch/powerpc/include/asm/nohash/pte-book3e.h b/arch/powerpc/include/asm/nohash/pte-book3e.h
> index 813918f40765..f798640422c2 100644
> --- a/arch/powerpc/include/asm/nohash/pte-book3e.h
> +++ b/arch/powerpc/include/asm/nohash/pte-book3e.h
> @@ -48,7 +48,7 @@
>   #define _PAGE_WRITETHRU	0x800000 /* W: cache write-through */
>   
>   /* "Higher level" linux bit combinations */
> -#define _PAGE_EXEC		_PAGE_BAP_UX /* .. and was cache cleaned */
> +#define _PAGE_EXEC		(_PAGE_BAP_SX | _PAGE_BAP_UX) /* .. and was cache cleaned */
>   #define _PAGE_RW		(_PAGE_BAP_SW | _PAGE_BAP_UW) /* User write permission */
>   #define _PAGE_KERNEL_RW		(_PAGE_BAP_SW | _PAGE_BAP_SR | _PAGE_DIRTY)
>   #define _PAGE_KERNEL_RO		(_PAGE_BAP_SR)
> @@ -93,11 +93,11 @@
>   /* Permission masks used to generate the __P and __S table */
>   #define PAGE_NONE	__pgprot(_PAGE_BASE)
>   #define PAGE_SHARED	__pgprot(_PAGE_BASE | _PAGE_USER | _PAGE_RW)
> -#define PAGE_SHARED_X	__pgprot(_PAGE_BASE | _PAGE_USER | _PAGE_RW | _PAGE_EXEC)
> +#define PAGE_SHARED_X	__pgprot(_PAGE_BASE | _PAGE_USER | _PAGE_RW | _PAGE_BAP_UX)
>   #define PAGE_COPY	__pgprot(_PAGE_BASE | _PAGE_USER)
> -#define PAGE_COPY_X	__pgprot(_PAGE_BASE | _PAGE_USER | _PAGE_EXEC)
> +#define PAGE_COPY_X	__pgprot(_PAGE_BASE | _PAGE_USER | _PAGE_BAP_UX)
>   #define PAGE_READONLY	__pgprot(_PAGE_BASE | _PAGE_USER)
> -#define PAGE_READONLY_X	__pgprot(_PAGE_BASE | _PAGE_USER | _PAGE_EXEC)
> +#define PAGE_READONLY_X	__pgprot(_PAGE_BASE | _PAGE_USER | _PAGE_BAP_UX)
>   
>   #ifndef __ASSEMBLY__
>   static inline pte_t pte_mkprivileged(pte_t pte)
> @@ -113,6 +113,16 @@ static inline pte_t pte_mkuser(pte_t pte)
>   }
>   
>   #define pte_mkuser pte_mkuser
> +
> +static inline pte_t pte_mkexec(pte_t pte)
> +{
> +	if (pte_val(pte) & _PAGE_BAP_UR)
> +		return __pte((pte_val(pte) & ~_PAGE_BAP_SX) | _PAGE_BAP_UX);
> +	else
> +		return __pte((pte_val(pte) & ~_PAGE_BAP_UX) | _PAGE_BAP_SX);
> +}
> +#define pte_mkexec pte_mkexec
> +
>   #endif /* __ASSEMBLY__ */
>   
>   #endif /* __KERNEL__ */
> diff --git a/arch/powerpc/mm/nohash/tlb_low_64e.S b/arch/powerpc/mm/nohash/tlb_low_64e.S
> index bf24451f3e71..9235e720e357 100644
> --- a/arch/powerpc/mm/nohash/tlb_low_64e.S
> +++ b/arch/powerpc/mm/nohash/tlb_low_64e.S
> @@ -222,7 +222,7 @@ tlb_miss_kernel_bolted:
>   
>   tlb_miss_fault_bolted:
>   	/* We need to check if it was an instruction miss */
> -	andi.	r10,r11,_PAGE_EXEC|_PAGE_BAP_SX
> +	andi.	r10,r11,_PAGE_BAP_UX|_PAGE_BAP_SX
>   	bne	itlb_miss_fault_bolted
>   dtlb_miss_fault_bolted:
>   	tlb_epilog_bolted
> @@ -239,7 +239,7 @@ itlb_miss_fault_bolted:
>   	srdi	r15,r16,60		/* get region */
>   	bne-	itlb_miss_fault_bolted
>   
> -	li	r11,_PAGE_PRESENT|_PAGE_EXEC	/* Base perm */
> +	li	r11,_PAGE_PRESENT|_PAGE_BAP_UX	/* Base perm */
>   
>   	/* We do the user/kernel test for the PID here along with the RW test
>   	 */
> @@ -614,7 +614,7 @@ itlb_miss_fault_e6500:
>   
>   	/* We do the user/kernel test for the PID here along with the RW test
>   	 */
> -	li	r11,_PAGE_PRESENT|_PAGE_EXEC	/* Base perm */
> +	li	r11,_PAGE_PRESENT|_PAGE_BAP_UX	/* Base perm */
>   	oris	r11,r11,_PAGE_ACCESSED@h
>   
>   	cmpldi	cr0,r15,0			/* Check for user region */
> @@ -734,7 +734,7 @@ normal_tlb_miss_done:
>   
>   normal_tlb_miss_access_fault:
>   	/* We need to check if it was an instruction miss */
> -	andi.	r10,r11,_PAGE_EXEC
> +	andi.	r10,r11,_PAGE_BAP_UX
>   	bne	1f
>   	ld	r14,EX_TLB_DEAR(r12)
>   	ld	r15,EX_TLB_ESR(r12)
>