Date: Wed, 22 May 2019 08:57:33 -0700 From: Thomas Garnier <thgarnie@...omium.org> To: "H . Peter Anvin" <hpa@...or.com> Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>, Kristen Carlson Accardi <kristen@...ux.intel.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, "the arch/x86 maintainers" <x86@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Nadav Amit <namit@...are.com>, Jann Horn <jannh@...gle.com>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v7 03/12] x86: Add macro to get symbol address for PIE support On Mon, May 20, 2019 at 8:13 PM <hpa@...or.com> wrote: > > On May 20, 2019 4:19:28 PM PDT, Thomas Garnier <thgarnie@...omium.org> wrote: > >From: Thomas Garnier <thgarnie@...gle.com> > > > >Add a new _ASM_MOVABS macro to fetch a symbol address. It will be used > >to replace "_ASM_MOV $<symbol>, %dst" code construct that are not > >compatible with PIE. > > > >Signed-off-by: Thomas Garnier <thgarnie@...gle.com> > >--- > > arch/x86/include/asm/asm.h | 1 + > > 1 file changed, 1 insertion(+) > > > >diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h > >index 3ff577c0b102..3a686057e882 100644 > >--- a/arch/x86/include/asm/asm.h > >+++ b/arch/x86/include/asm/asm.h > >@@ -30,6 +30,7 @@ > > #define _ASM_ALIGN __ASM_SEL(.balign 4, .balign 8) > > > > #define _ASM_MOV __ASM_SIZE(mov) > >+#define _ASM_MOVABS __ASM_SEL(movl, movabsq) > > #define _ASM_INC __ASM_SIZE(inc) > > #define _ASM_DEC __ASM_SIZE(dec) > > #define _ASM_ADD __ASM_SIZE(add) > > This is just about *always* wrong on x86-86. We should be using leaq sym(%rip),%reg. If it isn't reachable by leaq, then it is a non-PIE symbol like percpu. You do have to keep those distinct! Yes, I agree. This patch is just having a shortcut when it is a non-PIE symbol. The other patches try to separate the use cases where a leaq sym(%rip) would work versus the need for a movabsq. There are multiple cases where relative references are not possible because the memory layout is different (hibernation, early boot or others). > -- > Sent from my Android device with K-9 Mail. Please excuse my brevity.
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