shinys000114/linux
1
0
Fork 0
mirror of https://github.com/hardkernel/linux.git synced 2026-06-05 02:21:52 +09:00
Code Issues Packages Projects Releases Wiki Activity

x86/vdso: Prevent segfaults due to hoisted vclock reads

Browse Source 
commit ff17bbe0bb upstream.

GCC 5.5.0 sometimes cleverly hoists reads of the pvclock and/or hvclock
pages before the vclock mode checks.  This creates a path through
vclock_gettime() in which no vclock is enabled at all (due to disabled
TSC on old CPUs, for example) but the pvclock or hvclock page
nevertheless read.  This will segfault on bare metal.

This fixes commit 459e3a2153 ("gcc-9: properly declare the
{pv,hv}clock_page storage") in the sense that, before that commit, GCC
didn't seem to generate the offending code.  There was nothing wrong
with that commit per se, and -stable maintainers should backport this to
all supported kernels regardless of whether the offending commit was
present, since the same crash could just as easily be triggered by the
phase of the moon.

On GCC 9.1.1, this doesn't seem to affect the generated code at all, so
I'm not too concerned about performance regressions from this fix.

Cc: stable@vger.kernel.org
Cc: x86@kernel.org
Cc: Borislav Petkov <bp@alien8.de>
Reported-by: Duncan Roe <duncan_roe@optusnet.com.au>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Andy Lutomirski
2019-06-21 08:43:04 -07:00
committed by Greg Kroah-Hartman
parent f73e824544
commit 2c04e80a6c
1 changed files with 13 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
arch/x86/entry/vdso/vclock_gettime.c
View File

@@ -191,13 +191,24 @@ notrace static inline u64 vgetsns(int *mode)
if (gtod->vclock_mode == VCLOCK_TSC)
cycles = vread_tsc();
/*
* For any memory-mapped vclock type, we need to make sure that gcc
* doesn't cleverly hoist a load before the mode check. Otherwise we
* might end up touching the memory-mapped page even if the vclock in
* question isn't enabled, which will segfault. Hence the barriers.
*/
#ifdef CONFIG_PARAVIRT_CLOCK
else if (gtod->vclock_mode == VCLOCK_PVCLOCK)
else if (gtod->vclock_mode == VCLOCK_PVCLOCK) {
barrier();
cycles = vread_pvclock(mode);
}
#endif
#ifdef CONFIG_HYPERV_TSCPAGE
else if (gtod->vclock_mode == VCLOCK_HVCLOCK)
else if (gtod->vclock_mode == VCLOCK_HVCLOCK) {
barrier();
cycles = vread_hvclock(mode);
}
#endif
else
return 0;