From: Dave Martin <Dave.Martin@arm.com>
To: Vladimir Murzin <vladimir.murzin@arm.com>
Cc: catalin.marinas@arm.com, keescook@chromium.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 2/2] arm64: Introduce HWCAPS2_EXECONLY
Date: Tue, 8 Dec 2020 16:36:16 +0000 [thread overview]
Message-ID: <20201208163614.GS6882@arm.com> (raw)
In-Reply-To: <20201119133953.15585-3-vladimir.murzin@arm.com>
On Thu, Nov 19, 2020 at 01:39:53PM +0000, Vladimir Murzin wrote:
> With EPAN supported it might be handy to user know that PROT_EXEC
> gives execute-only permission, so advertise it via HWCAPS2_EXECONLY
>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
> ---
> arch/arm64/include/asm/hwcap.h | 1 +
> arch/arm64/include/asm/sysreg.h | 1 +
> arch/arm64/include/uapi/asm/hwcap.h | 1 +
> arch/arm64/kernel/cpufeature.c | 3 +++
> arch/arm64/kernel/cpuinfo.c | 1 +
> 5 files changed, 7 insertions(+)
>
> diff --git a/arch/arm64/include/asm/hwcap.h b/arch/arm64/include/asm/hwcap.h
> index 9a5498c..5ee5bce 100644
> --- a/arch/arm64/include/asm/hwcap.h
> +++ b/arch/arm64/include/asm/hwcap.h
> @@ -105,6 +105,7 @@
> #define KERNEL_HWCAP_RNG __khwcap2_feature(RNG)
> #define KERNEL_HWCAP_BTI __khwcap2_feature(BTI)
> #define KERNEL_HWCAP_MTE __khwcap2_feature(MTE)
> +#define KERNEL_HWCAP_EXECONLY __khwcap2_feature(EXECONLY)
Should this definitely be an hwcap?
[Apologies if I already made this comment, but if I did I can't find a
record of it, so here it is again (or not)]:
This seems to have the wrong semantics for hwcaps: it's not a (purely) a
property of the hardware, not an arch-specific concept, and old code
that doesn't know about this flag may not work properly when the flag
is set.
Software that requires that any memory mapped without PROT_READ is
readable would be nonportable according to POSIX, but nonportable
doesn't mean not correct; it just means that POSIX doesn't gurarantee
that it works everywhere.
So:
1) Is true execute-only memory an ABI break that we care about, and do
we need an explicit opt-in?
2) Otherwise, is there another more suitable and less arch-specific
mechanism that could be used? (Maybe AT_FLAGS or similar?)
This issue may have come up on other arches. I've not gone digging.
Cheers
---Dave
[...]
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next prev parent reply other threads:[~2020-12-08 16:38 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-19 13:39 [PATCH 0/2] arm64: Support Enhanced PAN Vladimir Murzin
2020-11-19 13:39 ` [PATCH 1/2] arm64: Support execute-only permissions with " Vladimir Murzin
2020-11-19 18:22 ` Catalin Marinas
2020-11-19 18:52 ` Dave Martin
2020-11-27 18:31 ` Catalin Marinas
2020-12-02 18:23 ` Catalin Marinas
2020-12-08 11:41 ` Vladimir Murzin
2020-11-19 13:39 ` [PATCH 2/2] arm64: Introduce HWCAPS2_EXECONLY Vladimir Murzin
2020-12-08 16:36 ` Dave Martin [this message]
2020-12-08 17:34 ` Catalin Marinas
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