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Date:   Mon, 10 Oct 2022 14:03:09 -0600
From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
To:     Michael Ellerman <mpe@ellerman.id.au>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>, ajd@linux.ibm.com,
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Subject: Re: [GIT PULL] Please pull powerpc/linux.git powerpc-6.1-1 tag
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On Mon, Oct 10, 2022 at 01:25:25PM -0600, Jason A. Donenfeld wrote:
> Hi Michael,
> 
> On Sun, Oct 09, 2022 at 10:01:39PM +1100, Michael Ellerman wrote:
> > powerpc updates for 6.1
> > 
> >  - Remove our now never-true definitions for pgd_huge() and p4d_leaf().
> > 
> >  - Add pte_needs_flush() and huge_pmd_needs_flush() for 64-bit.
> > 
> >  - Add support for syscall wrappers.
> > 
> >  - Add support for KFENCE on 64-bit.
> > 
> >  - Update 64-bit HV KVM to use the new guest state entry/exit accounting API.
> > 
> >  - Support execute-only memory when using the Radix MMU (P9 or later).
> > 
> >  - Implement CONFIG_PARAVIRT_TIME_ACCOUNTING for pseries guests.
> > 
> >  - Updates to our linker script to move more data into read-only sections.
> > 
> >  - Allow the VDSO to be randomised on 32-bit.
> > 
> >  - Many other small features and fixes.
> 
> FYI, something in here broke the wireguard test suite, which runs the
> iperf3 networking utility. The full log is here [1], but the relevant part
> is: 
> 
> [+] NS1: iperf3 -Z -t 3 -c 192.168.241.2
> Connecting to host 192.168.241.2, port 5201
> iperf3: error - failed to read /dev/urandom: Bad address
> 
> I'll see if I can narrow it down a bit more and bisect. But just FYI, in
> case you have an intuition.

Huh. From iov_iter.c:

static int copyout(void __user *to, const void *from, size_t n)
{
        size_t before = n;
        if (should_fail_usercopy())
                return n;
        if (access_ok(to, n)) {
                instrument_copy_to_user(to, from, n);
                n = raw_copy_to_user(to, from, n);
                if (n == before)
                        pr_err("SARU n still %zu pointer is %lx\n", n, (unsigned long)to);
        }
        return n;
}

I added the pr_err() there to catch the failure:
[    3.443506] SARU n still 64 pointer is b78db000

Also I managed to extract the failing portion of iperf3 into something
smaller:

        int temp;
        char *x;
        ssize_t l;
        FILE *f;
        char template[] = "/blah-XXXXXX";

        temp = mkstemp(template);
        if (temp < 0)
                panic("mkstemp");
        if (unlink(template) < 0)
                panic("unlink");
        if (ftruncate(temp, 0x20000) < 0)
                panic("ftruncate");
        x = mmap(NULL, 0x20000, PROT_READ|PROT_WRITE, MAP_PRIVATE, temp, 0);
        if (x == MAP_FAILED)
                panic("mmap");
        f = fopen("/dev/urandom", "rb");
        if (!f)
                panic("fopen");
        setbuf(f, NULL);
        if (fread(x, 1, 0x20000, f) != 0x20000)
                panic("fread");

Jason