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From: Dave Martin <Dave.Martin@arm.com>
To: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Cc: linux-man@vger.kernel.org, linux-arch@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 02/14] prctl.2: Add health warning
Date: Wed, 13 May 2020 12:41:38 +0100	[thread overview]
Message-ID: <20200513114137.GJ21779@arm.com> (raw)
In-Reply-To: <7218089f-20df-52b3-e1d4-ac63e0215efc@gmail.com>

On Wed, May 13, 2020 at 01:40:26PM +0200, Michael Kerrisk (man-pages) wrote:
> Hi Dave,
> 
> On 5/13/20 1:13 PM, Dave Martin wrote:
> > On Wed, May 13, 2020 at 12:10:25PM +0200, Michael Kerrisk (man-pages) wrote:
> >> Hi Dave,
> >>
> >> On 5/12/20 6:36 PM, Dave Martin wrote:
> >>> In reality, almost every prctl interferes with assumptions that the
> >>> compiler and C library / runtime rely on.  prctl() can therefore
> >>> make userspace explode in a variety ways that are likely to be hard
> >>> to debug.
> >>>
> >>> This is not obvious to the uninitiated, so add a warning.
> >>
> >> Patch applied. But see my comments on patch 04. I may want to 
> >> circle back on this patch later, since the wording feels a 
> >> little strong to me (we simply must use prctl for some things, 
> >> and not all of those things break user-space/runtime as far 
> >> as I know). If you have some thoughts on softening the warning,
> >> let me know.
> > 
> > Certainly the "if at all" can go -- this was just a suggestion
> > really.
> 
> Yes. Gone.
> 
> > Maybe the whole thing is superfluous.  In C anything can screw up the
> > runtime if you try hard enough.
> 
> I think it's at least worth alerting the reader to this issue.
> 
> > The background to this patch is that things like the new
> > PR_PAC_RESET_KEYS and PR_SVE_SET_VL are likely to crash the program, or
> > place a timebomb that will explode later when someone upgrades their
> > toolchain or links with a new version of some library.  Many existing
> > prctls that look equally unfriendly...
> > 
> > I didn't want to say nothing at all, but I didn't want to get into the
> > gory details either.
> 
> (Okay.)
> 
> > Doing the digging to document the safety requirements of each prctl
> > would be a lot of work, and probably an exercise in futility anyway --
> > how to use a lot of prctls safely depends on the run-time environment as
> > much as it does on the kernel.
> > 
> > 
> > If you want to drop this, I'm happy to add explicit notes to just the
> > new arm64 prctls instead for now.
> 
> I just softened the warning a little; see below. Explicit notes for
> the new arm64 prctls would certainly be welcome.

OK, that works for me.  I'll try to keep it brief.

Cheers
---Dave

  reply	other threads:[~2020-05-13 11:41 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-12 16:36 [PATCH 00/14] prctl.2 man page updates for Linux 5.6 Dave Martin
2020-05-12 16:36 ` [PATCH 01/14] prctl.2: tfix clarify that prctl can apply to threads Dave Martin
2020-05-13  8:30   ` Michael Kerrisk (man-pages)
2020-05-12 16:36 ` [PATCH 02/14] prctl.2: Add health warning Dave Martin
2020-05-13 10:10   ` Michael Kerrisk (man-pages)
2020-05-13 11:13     ` Dave Martin
2020-05-13 11:40       ` Michael Kerrisk (man-pages)
2020-05-13 11:41         ` Dave Martin [this message]
2020-05-12 16:36 ` [PATCH 03/14] prctl.2: tfix mis-description of thread ID values in procfs Dave Martin
2020-05-13  8:36   ` Michael Kerrisk (man-pages)
2020-05-12 16:36 ` [PATCH 04/14] prctl.2: srcfix add comments for navigation Dave Martin
2020-05-13 10:09   ` Michael Kerrisk (man-pages)
2020-05-13 10:56     ` Dave Martin
2020-05-13 11:03       ` Michael Kerrisk (man-pages)
2020-05-13 11:15         ` Dave Martin
2020-05-13 11:48           ` Michael Kerrisk (man-pages)
2020-05-13 11:51             ` Dave Martin
2020-05-12 16:36 ` [PATCH 05/14] prctl.2: tfix listing order of prctls Dave Martin
2020-05-13 10:10   ` Michael Kerrisk (man-pages)
2020-05-13 11:21     ` Dave Martin
2020-05-13 11:31       ` Michael Kerrisk (man-pages)
2020-05-13 11:45         ` Dave Martin
2020-05-12 16:36 ` [PATCH 06/14] prctl.2: ffix quotation mark tweaks Dave Martin
2020-05-13 10:11   ` Michael Kerrisk (man-pages)
2020-05-13 11:39     ` Dave Martin
2020-05-13 11:46       ` Michael Kerrisk (man-pages)
2020-05-13 11:51         ` Dave Martin
2020-05-12 16:36 ` [PATCH 07/14] prctl.2: Document removal of Intel MPX prctls Dave Martin
2020-05-12 16:41   ` Dave Hansen
2020-05-13 10:11   ` Michael Kerrisk (man-pages)
2020-05-12 16:36 ` [PATCH 08/14] prctl.2: Work around bogus constant "maxsig" in PR_SET_PDEATHSIG Dave Martin
2020-05-13 10:30   ` Michael Kerrisk (man-pages)
2020-05-12 16:36 ` [PATCH 09/14] prctl.2: tfix minor punctuation in SPECULATION_CTRL prctls Dave Martin
2020-05-13 10:31   ` Michael Kerrisk (man-pages)
2020-05-12 16:36 ` [PATCH 10/14] prctl.2: Add PR_SPEC_INDIRECT_BRANCH for " Dave Martin
2020-05-13 11:21   ` Michael Kerrisk (man-pages)
2020-05-13 11:49     ` Dave Martin
2020-05-13 12:06       ` Michael Kerrisk (man-pages)
2020-05-13 13:53         ` Dave Martin
2020-05-12 16:36 ` [PATCH 11/14] prctl.2: Add PR_SPEC_DISABLE_NOEXEC " Dave Martin
2020-05-12 16:36 ` [PATCH 12/14] prctl.2: Clarify the unsupported hardware case of EINVAL Dave Martin
2020-05-13 10:48   ` Michael Kerrisk (man-pages)
2020-05-12 16:36 ` [PATCH 13/14] prctl.2: Add SVE prctls (arm64) Dave Martin
2020-05-13  8:43   ` Will Deacon
2020-05-13 10:46     ` Dave Martin
2020-05-13 11:01       ` Michael Kerrisk (man-pages)
2020-05-13 14:02         ` Dave Martin
2020-05-13 21:11           ` Will Deacon
2020-05-18 16:37             ` Dave Martin
2020-05-26 14:45             ` Dave Martin
2020-05-12 16:36 ` [PATCH 14/14] prctl.2: Add PR_PAC_RESET_KEYS (arm64) Dave Martin
2020-05-13  7:25   ` Will Deacon
2020-05-13 14:36     ` Dave Martin
2020-05-13 21:00       ` Will Deacon
2020-05-18 16:11         ` Dave Martin
2020-05-18 16:29           ` Will Deacon
2020-05-13 11:28 ` [PATCH 00/14] prctl.2 man page updates for Linux 5.6 Michael Kerrisk (man-pages)

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