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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, Andy Lutomirski <luto@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: [PATCH 4.18 18/44] x86/vdso: Fix asm constraints on vDSO syscall fallbacks
Date: Thu, 11 Oct 2018 17:39:56 +0200	[thread overview]
Message-ID: <20181011152453.282236451@linuxfoundation.org> (raw)
In-Reply-To: <20181011152452.571669983@linuxfoundation.org>

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andy Lutomirski <luto@kernel.org>

commit 715bd9d12f84d8f5cc8ad21d888f9bc304a8eb0b upstream.

The syscall fallbacks in the vDSO have incorrect asm constraints.
They are not marked as writing to their outputs -- instead, they are
marked as clobbering "memory", which is useless.  In particular, gcc
is smart enough to know that the timespec parameter hasn't escaped,
so a memory clobber doesn't clobber it.  And passing a pointer as an
asm *input* does not tell gcc that the pointed-to value is changed.

Add in the fact that the asm instructions weren't volatile, and gcc
was free to omit them entirely unless their sole output (the return
value) is used.  Which it is (phew!), but that stops happening with
some upcoming patches.

As a trivial example, the following code:

void test_fallback(struct timespec *ts)
{
	vdso_fallback_gettime(CLOCK_MONOTONIC, ts);
}

compiles to:

00000000000000c0 <test_fallback>:
  c0:   c3                      retq

To add insult to injury, the RCX and R11 clobbers on 64-bit
builds were missing.

The "memory" clobber is also unnecessary -- no ordering with respect to
other memory operations is needed, but that's going to be fixed in a
separate not-for-stable patch.

Fixes: 2aae950b21e4 ("x86_64: Add vDSO for x86-64 with gettimeofday/clock_gettime/getcpu")
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/2c0231690551989d2fafa60ed0e7b5cc8b403908.1538422295.git.luto@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/entry/vdso/vclock_gettime.c |   18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

--- a/arch/x86/entry/vdso/vclock_gettime.c
+++ b/arch/x86/entry/vdso/vclock_gettime.c
@@ -43,8 +43,9 @@ extern u8 hvclock_page
 notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
 {
 	long ret;
-	asm("syscall" : "=a" (ret) :
-	    "0" (__NR_clock_gettime), "D" (clock), "S" (ts) : "memory");
+	asm ("syscall" : "=a" (ret), "=m" (*ts) :
+	     "0" (__NR_clock_gettime), "D" (clock), "S" (ts) :
+	     "memory", "rcx", "r11");
 	return ret;
 }
 
@@ -52,8 +53,9 @@ notrace static long vdso_fallback_gtod(s
 {
 	long ret;
 
-	asm("syscall" : "=a" (ret) :
-	    "0" (__NR_gettimeofday), "D" (tv), "S" (tz) : "memory");
+	asm ("syscall" : "=a" (ret), "=m" (*tv), "=m" (*tz) :
+	     "0" (__NR_gettimeofday), "D" (tv), "S" (tz) :
+	     "memory", "rcx", "r11");
 	return ret;
 }
 
@@ -64,12 +66,12 @@ notrace static long vdso_fallback_gettim
 {
 	long ret;
 
-	asm(
+	asm (
 		"mov %%ebx, %%edx \n"
 		"mov %2, %%ebx \n"
 		"call __kernel_vsyscall \n"
 		"mov %%edx, %%ebx \n"
-		: "=a" (ret)
+		: "=a" (ret), "=m" (*ts)
 		: "0" (__NR_clock_gettime), "g" (clock), "c" (ts)
 		: "memory", "edx");
 	return ret;
@@ -79,12 +81,12 @@ notrace static long vdso_fallback_gtod(s
 {
 	long ret;
 
-	asm(
+	asm (
 		"mov %%ebx, %%edx \n"
 		"mov %2, %%ebx \n"
 		"call __kernel_vsyscall \n"
 		"mov %%edx, %%ebx \n"
-		: "=a" (ret)
+		: "=a" (ret), "=m" (*tv), "=m" (*tz)
 		: "0" (__NR_gettimeofday), "g" (tv), "c" (tz)
 		: "memory", "edx");
 	return ret;



  parent reply	other threads:[~2018-10-11 15:47 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-11 15:39 [PATCH 4.18 00/44] 4.18.14-stable review Greg Kroah-Hartman
2018-10-11 15:39 ` [PATCH 4.18 01/44] perf/core: Add sanity check to deal with pinned event failure Greg Kroah-Hartman
2018-10-11 15:39 ` [PATCH 4.18 02/44] mm: migration: fix migration of huge PMD shared pages Greg Kroah-Hartman
2018-10-11 15:39 ` [PATCH 4.18 03/44] mm, thp: fix mlocking THP page with migration enabled Greg Kroah-Hartman
2018-10-11 15:39 ` [PATCH 4.18 04/44] mm/vmstat.c: skip NR_TLB_REMOTE_FLUSH* properly Greg Kroah-Hartman
2018-10-11 15:39 ` [PATCH 4.18 05/44] KVM: x86: fix L1TFs MMIO GFN calculation Greg Kroah-Hartman
2018-10-11 15:39 ` [PATCH 4.18 06/44] KVM: VMX: check for existence of secondary exec controls before accessing Greg Kroah-Hartman
2018-10-11 15:39 ` [PATCH 4.18 07/44] blk-mq: I/O and timer unplugs are inverted in blktrace Greg Kroah-Hartman
2018-10-11 15:39 ` [PATCH 4.18 08/44] pstore/ram: Fix failure-path memory leak in ramoops_init Greg Kroah-Hartman
2018-10-11 15:39 ` [PATCH 4.18 09/44] clocksource/drivers/timer-atmel-pit: Properly handle error cases Greg Kroah-Hartman
2018-10-11 15:39 ` [PATCH 4.18 10/44] fbdev/omapfb: fix omapfb_memory_read infoleak Greg Kroah-Hartman
2018-10-11 15:39 ` [PATCH 4.18 11/44] xen-netback: fix input validation in xenvif_set_hash_mapping() Greg Kroah-Hartman
2018-10-11 15:39 ` [PATCH 4.18 12/44] mmc: core: Fix debounce time to use microseconds Greg Kroah-Hartman
2018-10-11 15:39 ` [PATCH 4.18 13/44] mmc: slot-gpio: Fix debounce time to use miliseconds again Greg Kroah-Hartman
2018-10-11 15:39 ` [PATCH 4.18 14/44] mac80211: allocate TXQs for active monitor interfaces Greg Kroah-Hartman
2018-10-11 15:39 ` [PATCH 4.18 15/44] drm/amdgpu: Fix vce work queue was not cancelled when suspend Greg Kroah-Hartman
2018-10-11 15:39 ` [PATCH 4.18 16/44] drm/syncobj: Dont leak fences when WAIT_FOR_SUBMIT is set Greg Kroah-Hartman
2018-10-11 15:39 ` [PATCH 4.18 17/44] drm: fix use-after-free read in drm_mode_create_lease_ioctl() Greg Kroah-Hartman
2018-10-11 15:39 ` Greg Kroah-Hartman [this message]
2018-10-11 15:39 ` [PATCH 4.18 19/44] selftests/x86: Add clock_gettime() tests to test_vdso Greg Kroah-Hartman
2018-10-11 15:39 ` [PATCH 4.18 20/44] x86/vdso: Only enable vDSO retpolines when enabled and supported Greg Kroah-Hartman
2018-10-11 15:39 ` [PATCH 4.18 21/44] x86/vdso: Fix vDSO syscall fallback asm constraint regression Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 22/44] PCI: Reprogram bridge prefetch registers on resume Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 23/44] mac80211: fix setting IEEE80211_KEY_FLAG_RX_MGMT for AP mode keys Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 24/44] PM / core: Clear the direct_complete flag on errors Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 25/44] dm mpath: fix attached_handler_name leak and dangling hw_handler_name pointer Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 26/44] dm cache metadata: ignore hints array being too small during resize Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 27/44] dm cache: fix resize crash if user doesnt reload cache table Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 28/44] xhci: Add missing CAS workaround for Intel Sunrise Point xHCI Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 29/44] usb: xhci-mtk: resume USB3 roothub first Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 30/44] USB: serial: simple: add Motorola Tetra MTP6550 id Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 31/44] USB: serial: option: improve Quectel EP06 detection Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 32/44] USB: serial: option: add two-endpoints device-id flag Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 33/44] usb: cdc_acm: Do not leak URB buffers Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 34/44] tty: Drop tty->count on tty_reopen() failure Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 35/44] of: unittest: Disable interrupt node tests for old world MAC systems Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 36/44] powerpc: Avoid code patching freed init sections Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 37/44] powerpc/lib: fix book3s/32 boot failure due to code patching Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 38/44] ARC: clone syscall to setp r25 as thread pointer Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 39/44] f2fs: fix invalid memory access Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 40/44] tipc: call start and done ops directly in __tipc_nl_compat_dumpit() Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 41/44] ucma: fix a use-after-free in ucma_resolve_ip() Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 42/44] ubifs: Check for name being NULL while mounting Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 43/44] rds: rds_ib_recv_alloc_cache() should call alloc_percpu_gfp() instead Greg Kroah-Hartman
2018-10-11 15:40 ` [PATCH 4.18 44/44] ath10k: fix scan crash due to incorrect length calculation Greg Kroah-Hartman
2018-10-11 22:34 ` [PATCH 4.18 00/44] 4.18.14-stable review Shuah Khan
2018-10-12  4:22 ` Naresh Kamboju
2018-10-12 10:24   ` Greg Kroah-Hartman
2018-10-12 15:43 ` Guenter Roeck

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