Re: [PATCH 4/8] arm64: Basic Branch Target Identification support

On Thu, Jun 06, 2019 at 10:34:22AM -0700, Yu-cheng Yu wrote:

On Thu, 2019-06-06 at 18:23 +0100, Dave Martin wrote:

quoted

On Thu, Jun 06, 2019 at 06:11:56PM +0100, Catalin Marinas wrote:

quoted

On Fri, May 24, 2019 at 03:53:06PM +0100, Dave P Martin wrote:

quoted

On Fri, May 24, 2019 at 02:02:17PM +0100, Mark Rutland wrote:

quoted

On Fri, May 24, 2019 at 11:25:29AM +0100, Dave Martin wrote:

quoted

 #endif /* _UAPI__ASM_HWCAP_H */

diff --git a/arch/arm64/include/uapi/asm/mman.h

b/arch/arm64/include/uapi/asm/mman.h
new file mode 100644
index 0000000..4776b43

--- /dev/null
+++ b/arch/arm64/include/uapi/asm/mman.h

@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI__ASM_MMAN_H
+#define _UAPI__ASM_MMAN_H
+
+#include <asm-generic/mman.h>
+
+#define PROT_BTI_GUARDED	0x10		/* BTI guarded

page */

From prior discussions, I thought this would be PROT_BTI, without the
_GUARDED suffix. Do we really need that?

AFAICT, all other PROT_* definitions only have a single underscore, and
the existing arch-specific flags are PROT_ADI on sparc, and PROT_SAO on
powerpc.

No strong opinon.  I was trying to make the name less obscure, but I'm
equally happy with PROT_BTI if people prefer that.

I prefer PROT_BTI as well. We are going to add a PROT_MTE at some point
(and a VM_ARM64_MTE in the high VMA flag bits).

Ack.

Some things need attention, so I need to respin this series anyway.

skip_faulting_instruction() and kprobes/uprobes may need looking at,
plus I want to simply the ELF parsing (at least to skip some cost for
arm64).

Can we add a case in the 'consistency checks for the interpreter' (right above
where you add arch_parse_property()) for PT_NOTE?  That way you can still use
part of the same parser.

I think for arm64 that we can skip searching all the notes by checking
for a PT_GNU_PROPERTY entry; once that's found, the actual
NT_GNU_PROPERTY_TYPE_0 parsing should be common.  If there's no
PT_GNU_PROPERTY entry, we can immediately give up.

For x86, would it makes sense to use PT_GNU_PROPERTY if it's there,
and fall back to scanning all the notes otherwise?  Ideally we
wouldn't need the fallback, but if there are binaries in the wild with
NT_GNU_PROPERTY_TYPE_0 that lack a PT_GNU_PROPERTY entry, we may be
stuck with that.

Thoughts?

Cheers
---Dave

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