linux-cve-announce - CVE-2025-37991: parisc: Fix double SIGFPE crash

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Message-ID: <2025052000-CVE-2025-37991-c6dc@gregkh>
Date: Tue, 20 May 2025 19:17:02 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-37991: parisc: Fix double SIGFPE crash

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

parisc: Fix double SIGFPE crash

Camm noticed that on parisc a SIGFPE exception will crash an application with
a second SIGFPE in the signal handler.  Dave analyzed it, and it happens
because glibc uses a double-word floating-point store to atomically update
function descriptors. As a result of lazy binding, we hit a floating-point
store in fpe_func almost immediately.

When the T bit is set, an assist exception trap occurs when when the
co-processor encounters *any* floating-point instruction except for a double
store of register %fr0.  The latter cancels all pending traps.  Let's fix this
by clearing the Trap (T) bit in the FP status register before returning to the
signal handler in userspace.

The issue can be reproduced with this test program:

root@...isc:~# cat fpe.c

static void fpe_func(int sig, siginfo_t *i, void *v) {
        sigset_t set;
        sigemptyset(&set);
        sigaddset(&set, SIGFPE);
        sigprocmask(SIG_UNBLOCK, &set, NULL);
        printf("GOT signal %d with si_code %ld\n", sig, i->si_code);
}

int main() {
        struct sigaction action = {
                .sa_sigaction = fpe_func,
                .sa_flags = SA_RESTART|SA_SIGINFO };
        sigaction(SIGFPE, &action, 0);
        feenableexcept(FE_OVERFLOW);
        return printf("%lf\n",1.7976931348623158E308*1.7976931348623158E308);
}

root@...isc:~# gcc fpe.c -lm
root@...isc:~# ./a.out
 Floating point exception

root@...isc:~# strace -f ./a.out
 execve("./a.out", ["./a.out"], 0xf9ac7034 /* 20 vars */) = 0
 getrlimit(RLIMIT_STACK, {rlim_cur=8192*1024, rlim_max=RLIM_INFINITY}) = 0
 ...
 rt_sigaction(SIGFPE, {sa_handler=0x1110a, sa_mask=[], sa_flags=SA_RESTART|SA_SIGINFO}, NULL, 8) = 0
 --- SIGFPE {si_signo=SIGFPE, si_code=FPE_FLTOVF, si_addr=0x1078f} ---
 --- SIGFPE {si_signo=SIGFPE, si_code=FPE_FLTOVF, si_addr=0xf8f21237} ---
 +++ killed by SIGFPE +++
 Floating point exception

The Linux kernel CVE team has assigned CVE-2025-37991 to this issue.


Affected and fixed versions
===========================

	Fixed in 5.15.182 with commit ec4584495868bd465fe60a3f771915c0e7ce7951
	Fixed in 6.1.138 with commit 6c639af49e9e5615a8395981eaf5943fb40acd6f
	Fixed in 6.6.90 with commit 6a098c51d18ec99485668da44294565c43dbc106
	Fixed in 6.12.28 with commit cf21e890f56b7d0038ddaf25224e4f4c69ecd143
	Fixed in 6.14.6 with commit df3592e493d7f29bae4ffde9a9325de50ddf962e
	Fixed in 6.15-rc5 with commit de3629baf5a33af1919dec7136d643b0662e85ef

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-37991
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	arch/parisc/math-emu/driver.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/ec4584495868bd465fe60a3f771915c0e7ce7951
	https://git.kernel.org/stable/c/6c639af49e9e5615a8395981eaf5943fb40acd6f
	https://git.kernel.org/stable/c/6a098c51d18ec99485668da44294565c43dbc106
	https://git.kernel.org/stable/c/cf21e890f56b7d0038ddaf25224e4f4c69ecd143
	https://git.kernel.org/stable/c/df3592e493d7f29bae4ffde9a9325de50ddf962e
	https://git.kernel.org/stable/c/de3629baf5a33af1919dec7136d643b0662e85ef