On Tue, Jun 11, 2019 at 7:39 PM Catalin Marinas [off-list ref] wrote:

On Tue, Jun 11, 2019 at 07:09:46PM +0200, Andrey Konovalov wrote:

quoted

On Tue, Jun 11, 2019 at 4:57 PM Catalin Marinas [off-list ref] wrote:

quoted

On Mon, Jun 10, 2019 at 06:53:27PM +0100, Catalin Marinas wrote:

quoted

On Mon, Jun 03, 2019 at 06:55:04PM +0200, Andrey Konovalov wrote:

quoted

diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index e5d5f31c6d36..9164ecb5feca 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h

@@ -94,7 +94,7 @@ static inline unsigned long __range_ok(const void __user *addr, unsigned long si
    return ret;
 }

-#define access_ok(addr, size)      __range_ok(addr, size)
+#define access_ok(addr, size)      __range_ok(untagged_addr(addr), size)

I'm going to propose an opt-in method here (RFC for now). We can't have
a check in untagged_addr() since this is already used throughout the
kernel for both user and kernel addresses (khwasan) but we can add one
in __range_ok(). The same prctl() option will be used for controlling
the precise/imprecise mode of MTE later on. We can use a TIF_ flag here
assuming that this will be called early on and any cloned thread will
inherit this.

Updated patch, inlining it below. Once we agreed on the approach, I
think Andrey can insert in in this series, probably after patch 2. The
differences from the one I posted yesterday:

- renamed PR_* macros together with get/set variants and the possibility
  to disable the relaxed ABI

- sysctl option - /proc/sys/abi/tagged_addr to disable the ABI globally
  (just the prctl() opt-in, tasks already using it won't be affected)

And, of course, it needs more testing.

Sure, I'll add it to the series.

Should I drop access_ok() change from my patch, since yours just reverts it?

Not necessary, your patch just relaxes the ABI for all apps, mine
tightens it. You could instead move the untagging to __range_ok() and
rebase my patch accordingly.

OK, will do. I'll also add a comment next to TIF_TAGGED_ADDR as Vincenzo asked.

--
Catalin

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