Commit 65973dd3 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar

selftests/x86/ldt_gdt_32: Work around a glibc sigaction() bug

i386 glibc is buggy and calls the sigaction syscall incorrectly.

This is asymptomatic for normal programs, but it blows up on
programs that do evil things with segmentation.  The ldt_gdt
self-test is an example of such an evil program.

This doesn't appear to be a regression -- I think I just got lucky
with the uninitialized memory that glibc threw at the kernel when I
wrote the test.

This hackish fix manually issues sigaction(2) syscalls to undo the
damage.  Without the fix, ldt_gdt_32 segfaults; with the fix, it
passes for me.

See: https://sourceware.org/bugzilla/show_bug.cgi?id=21269Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Garnier <thgarnie@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/aaab0f9f93c9af25396f01232608c163a760a668.1490218061.git.luto@kernel.orgSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent ef37bc36
......@@ -409,6 +409,51 @@ static void *threadproc(void *ctx)
}
}
#ifdef __i386__
#ifndef SA_RESTORE
#define SA_RESTORER 0x04000000
#endif
/*
* The UAPI header calls this 'struct sigaction', which conflicts with
* glibc. Sigh.
*/
struct fake_ksigaction {
void *handler; /* the real type is nasty */
unsigned long sa_flags;
void (*sa_restorer)(void);
unsigned char sigset[8];
};
static void fix_sa_restorer(int sig)
{
struct fake_ksigaction ksa;
if (syscall(SYS_rt_sigaction, sig, NULL, &ksa, 8) == 0) {
/*
* glibc has a nasty bug: it sometimes writes garbage to
* sa_restorer. This interacts quite badly with anything
* that fiddles with SS because it can trigger legacy
* stack switching. Patch it up. See:
*
* https://sourceware.org/bugzilla/show_bug.cgi?id=21269
*/
if (!(ksa.sa_flags & SA_RESTORER) && ksa.sa_restorer) {
ksa.sa_restorer = NULL;
if (syscall(SYS_rt_sigaction, sig, &ksa, NULL,
sizeof(ksa.sigset)) != 0)
err(1, "rt_sigaction");
}
}
}
#else
static void fix_sa_restorer(int sig)
{
/* 64-bit glibc works fine. */
}
#endif
static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
int flags)
{
......@@ -420,6 +465,7 @@ static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
if (sigaction(sig, &sa, 0))
err(1, "sigaction");
fix_sa_restorer(sig);
}
static jmp_buf jmpbuf;
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment