linux-kernel - Re: BTI interaction between seccomp filters in systemd and glibc mprotect calls, causing service failures

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Date:   Mon, 26 Oct 2020 17:45:42 +0100
From:   Florian Weimer <fweimer@...hat.com>
To:     Dave Martin via Libc-alpha <libc-alpha@...rceware.org>
Cc:     Jeremy Linton <jeremy.linton@....com>,
        Dave Martin <Dave.Martin@....com>,
        Mark Rutland <mark.rutland@....com>,
        systemd-devel@...ts.freedesktop.org,
        Kees Cook <keescook@...omium.org>,
        Catalin Marinas <Catalin.Marinas@....com>,
        Will Deacon <will.deacon@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>, toiwoton@...il.com,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: BTI interaction between seccomp filters in systemd and glibc
 mprotect calls, causing service failures

* Dave Martin via Libc-alpha:

> Would it now help to add something like:
>
> int mchangeprot(void *addr, size_t len, int old_flags, int new_flags)
> {
> 	int ret = -EINVAL;
> 	mmap_write_lock(current->mm);
> 	if (all vmas in [addr .. addr + len) have
> 			their mprotect flags set to old_flags) {
>
> 		ret = mprotect(addr, len, new_flags);
> 	}
> 	
> 	mmap_write_unlock(current->mm);
> 	return ret;
> }

I suggested something similar as well.  Ideally, the interface would
subsume pkey_mprotect, though, and have a separate flags argument from
the protection flags.  But then we run into argument list length limits.

Thanks,
Florian
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