linux-kernel - Re: [PATCH v10 11/40] arm64/mm: Allocate PIE slots for EL0 guarded control stack

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Message-ID: <Zr9fWfRObI5TNNXg@arm.com>
Date: Fri, 16 Aug 2024 15:16:57 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Mark Brown <broonie@...nel.org>
Cc: Will Deacon <will@...nel.org>, Jonathan Corbet <corbet@....net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marc Zyngier <maz@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	James Morse <james.morse@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Arnd Bergmann <arnd@...db.de>, Oleg Nesterov <oleg@...hat.com>,
	Eric Biederman <ebiederm@...ssion.com>,
	Shuah Khan <shuah@...nel.org>,
	"Rick P. Edgecombe" <rick.p.edgecombe@...el.com>,
	Deepak Gupta <debug@...osinc.com>, Ard Biesheuvel <ardb@...nel.org>,
	Szabolcs Nagy <Szabolcs.Nagy@....com>, Kees Cook <kees@...nel.org>,
	"H.J. Lu" <hjl.tools@...il.com>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Florian Weimer <fweimer@...hat.com>,
	Christian Brauner <brauner@...nel.org>,
	Thiago Jung Bauermann <thiago.bauermann@...aro.org>,
	Ross Burton <ross.burton@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
	kvmarm@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
	linux-arch@...r.kernel.org, linux-mm@...ck.org,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v10 11/40] arm64/mm: Allocate PIE slots for EL0 guarded
 control stack

On Thu, Aug 01, 2024 at 01:06:38PM +0100, Mark Brown wrote:
> diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
> index b11cfb9fdd37..545d54c88520 100644
> --- a/arch/arm64/include/asm/pgtable-prot.h
> +++ b/arch/arm64/include/asm/pgtable-prot.h
> @@ -144,15 +144,23 @@ static inline bool __pure lpa2_is_enabled(void)
>  /* 6:                                PTE_PXN | PTE_WRITE            */
>  /* 7: PAGE_SHARED_EXEC               PTE_PXN | PTE_WRITE | PTE_USER */
>  /* 8: PAGE_KERNEL_ROX      PTE_UXN                                  */
> -/* 9:                      PTE_UXN |                       PTE_USER */
> +/* 9: PAGE_GCS_RO          PTE_UXN |                       PTE_USER */
>  /* a: PAGE_KERNEL_EXEC     PTE_UXN |           PTE_WRITE            */
> -/* b:                      PTE_UXN |           PTE_WRITE | PTE_USER */
> +/* b: PAGE_GCS             PTE_UXN |           PTE_WRITE | PTE_USER */
>  /* c: PAGE_KERNEL_RO       PTE_UXN | PTE_PXN                        */
>  /* d: PAGE_READONLY        PTE_UXN | PTE_PXN |             PTE_USER */
>  /* e: PAGE_KERNEL          PTE_UXN | PTE_PXN | PTE_WRITE            */
>  /* f: PAGE_SHARED          PTE_UXN | PTE_PXN | PTE_WRITE | PTE_USER */
>  
> +#define _PAGE_GCS	(_PAGE_DEFAULT | PTE_NG | PTE_UXN | PTE_WRITE | PTE_USER)
> +#define _PAGE_GCS_RO	(_PAGE_DEFAULT | PTE_NG | PTE_UXN | PTE_USER)
> +
> +#define PAGE_GCS	__pgprot(_PAGE_GCS)
> +#define PAGE_GCS_RO	__pgprot(_PAGE_GCS_RO)
> +
>  #define PIE_E0	( \
> +	PIRx_ELx_PERM(pte_pi_index(_PAGE_GCS),           PIE_GCS)  | \
> +	PIRx_ELx_PERM(pte_pi_index(_PAGE_GCS_RO),        PIE_R)   | \
>  	PIRx_ELx_PERM(pte_pi_index(_PAGE_EXECONLY),      PIE_X_O) | \
>  	PIRx_ELx_PERM(pte_pi_index(_PAGE_READONLY_EXEC), PIE_RX)  | \
>  	PIRx_ELx_PERM(pte_pi_index(_PAGE_SHARED_EXEC),   PIE_RWX) | \
> @@ -160,6 +168,8 @@ static inline bool __pure lpa2_is_enabled(void)
>  	PIRx_ELx_PERM(pte_pi_index(_PAGE_SHARED),        PIE_RW))
>  
>  #define PIE_E1	( \
> +	PIRx_ELx_PERM(pte_pi_index(_PAGE_GCS),           PIE_NONE_O) | \
> +	PIRx_ELx_PERM(pte_pi_index(_PAGE_GCS_RO),        PIE_NONE_O) | \

It's fine to keep PIE_NONE_O here, the kernel wouldn't need to access
this memory with unprivileged instructions (it only matters for the
futex code using LDXR/STXR).

Reviewed-by: Catalin Marinas <catalin.marinas@....com>