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Date: Thu, 14 Feb 2019 16:23:53 +0530 From: Amit Daniel Kachhap <amit.kachhap@....com> To: Kristina Martsenko <kristina.martsenko@....com>, James Morse <james.morse@....com> Cc: linux-arm-kernel@...ts.infradead.org, Marc Zyngier <marc.zyngier@....com>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, kvmarm@...ts.cs.columbia.edu, Ramana Radhakrishnan <ramana.radhakrishnan@....com>, Dave Martin <Dave.Martin@....com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH v5 1/5] arm64: Add utilities to save restore pointer authentication keys Hi, On 2/13/19 11:02 PM, Kristina Martsenko wrote: > On 31/01/2019 16:20, James Morse wrote: >> Hi Amit, >> >> On 28/01/2019 06:58, Amit Daniel Kachhap wrote: >>> The keys can be switched either inside an assembly or such >>> functions which do not have pointer authentication checks, so a GCC >>> attribute is added to enable it. >>> >>> A function ptrauth_keys_store is added which is similar to existing >>> function ptrauth_keys_switch but saves the key values in memory. >>> This may be useful for save/restore scenarios when CPU changes >>> privilege levels, suspend/resume etc. >> >> >>> diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h >>> index 15d4951..98441ce 100644 >>> --- a/arch/arm64/include/asm/pointer_auth.h >>> +++ b/arch/arm64/include/asm/pointer_auth.h >>> @@ -11,6 +11,13 @@ >>> >>> #ifdef CONFIG_ARM64_PTR_AUTH >>> /* >>> + * Compile the function without pointer authentication instructions. This >>> + * allows pointer authentication to be enabled/disabled within the function >>> + * (but leaves the function unprotected by pointer authentication). >>> + */ >>> +#define __no_ptrauth __attribute__((target("sign-return-address=none"))) >> >> The documentation[0] for this says 'none' is the default. Will this only >> take-effect once the kernel supports pointer-auth for the host? (Is this just >> documentation until then?) > > Yes, I don't think this should be in this series, since we're not > building the kernel with pointer auth yet. I added it to stress on some functions which should be pointer authentication safe. Yes this can be dropped and a small comment may also do. //Amit D > >> >> ('noptrauth' would fit with 'notrace' slightly better) > > (But worse with e.g. __noreturn, __notrace_funcgraph, __init, > __always_inline, __exception. Not sure what the pattern is. Would > __noptrauth be better?) > > Thanks, > Kristina > >> >> [0] >> https://gcc.gnu.org/onlinedocs/gcc/AArch64-Function-Attributes.html#AArch64-Function-Attributes >> >
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