[PATCH v2 2/3] arm64: Enable BTI for main executable as well as the interpreter

[Mark Brown]

On Wed, Jun 09, 2021 at 04:17:13PM +0100, Dave Martin wrote:
> On Fri, Jun 04, 2021 at 12:24:49PM +0100, Mark Brown wrote:

> > -		if (system_supports_bti() && has_interp == is_interp &&
> > -		    (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI))
> > -			arch->flags |= ARM64_ELF_BTI;
> > +		if (system_supports_bti() &&
> > +		    (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) {
> > +			if (is_interp) {
> > +				arch->flags |= ARM64_ELF_INTERP_BTI;
> > +			} else {
> > +				arch->flags |= ARM64_ELF_EXEC_BTI;
> > +			}

> Nit: surplus curlies? (coding-style.rst does actually say to drop them
> when all branches of an if are single-statement one-liners -- I had
> presumed I was just being pedantic...)

I really think this hurts readability with the nested if inside
another if with a multi-line condition.

> > -	if (prot & PROT_EXEC)
> > -		prot |= PROT_BTI;
> > +		if (state->flags & ARM64_ELF_EXEC_BTI && !is_interp)
> > +			prot |= PROT_BTI;
> > +	}

> Is it worth adding () around the bitwise-& expressions?  I'm always a
> little uneasy about the operator precedence of binary &, although
> without looking it up I think you're correct.

Sure.  I'm fairly sure the compiler would've complained about
this case if it were ambiguous, I'm vaguely surprised it didn't
already.

> Feel free to adopt if this appeals to you, otherwise I'm also fine with
> your version.)

I'll see what I think when I get back to looking at this
properly.
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