linux-kernel - [patch 5/5] arm64: compat: vdso: Use legacy syscalls as fallback

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Message-Id: <20190728131648.971361611@linutronix.de>
Date:   Sun, 28 Jul 2019 15:12:56 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Andy Lutomirski <luto@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Paul Bolle <pebolle@...cali.nl>, Will Deacon <will@...nel.org>
Subject: [patch 5/5] arm64: compat: vdso: Use legacy syscalls as fallback

The generic VDSO implementation uses the Y2038 safe clock_gettime64() and
clock_getres_time64() syscalls as fallback for 32bit VDSO. This breaks
seccomp setups because these syscalls might be not (yet) allowed.

Implement the 32bit variants which use the legacy syscalls and select the
variant in the core library.

The 64bit time variants are not removed because they are required for the
time64 based vdso accessors.

Reported-by: Sean Christopherson <sean.j.christopherson@...el.com>
Reported-by: Paul Bolle <pebolle@...cali.nl>
Suggested-by: Andy Lutomirski <luto@...nel.org>
Fixes: 00b26474c2f1 ("lib/vdso: Provide generic VDSO implementation")
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
Note:

The NULL pointer check in the getres/getres32() fallbacks is just wrong.
The proper return code for a NULL pointer is -EFAULT. How did this ever
pass any posix test? Also it just should go away because any other invalid
pointer will be caught in the syscall anyway. The clockid check is also
part of the syscall so no point in having it here again. Handling calls
with invalid arguments is not really a performance critical operation.

---
 arch/arm64/include/asm/vdso/compat_gettimeofday.h |   40 ++++++++++++++++++++++
 1 file changed, 40 insertions(+)

--- a/arch/arm64/include/asm/vdso/compat_gettimeofday.h
+++ b/arch/arm64/include/asm/vdso/compat_gettimeofday.h
@@ -16,6 +16,8 @@
 
 #define VDSO_HAS_CLOCK_GETRES		1
 
+#define VDSO_HAS_32BIT_FALLBACK		1
+
 static __always_inline
 int gettimeofday_fallback(struct __kernel_old_timeval *_tv,
 			  struct timezone *_tz)
@@ -52,6 +54,23 @@ long clock_gettime_fallback(clockid_t _c
 }
 
 static __always_inline
+long clock_gettime32_fallback(clockid_t _clkid, struct old_timespec32 *_ts)
+{
+	register struct old_timespec32 *ts asm("r1") = _ts;
+	register clockid_t clkid asm("r0") = _clkid;
+	register long ret asm ("r0");
+	register long nr asm("r7") = __NR_compat_clock_gettime;
+
+	asm volatile(
+	"	swi #0\n"
+	: "=r" (ret)
+	: "r" (clkid), "r" (ts), "r" (nr)
+	: "memory");
+
+	return ret;
+}
+
+static __always_inline
 int clock_getres_fallback(clockid_t _clkid, struct __kernel_timespec *_ts)
 {
 	register struct __kernel_timespec *ts asm("r1") = _ts;
@@ -61,6 +80,27 @@ int clock_getres_fallback(clockid_t _clk
 
 	/* The checks below are required for ABI consistency with arm */
 	if ((_clkid >= MAX_CLOCKS) && (_ts == NULL))
+		return -EINVAL;
+
+	asm volatile(
+	"       swi #0\n"
+	: "=r" (ret)
+	: "r" (clkid), "r" (ts), "r" (nr)
+	: "memory");
+
+	return ret;
+}
+
+static __always_inline
+int clock_getres32_fallback(clockid_t _clkid, struct old_timespec32 *_ts)
+{
+	register struct old_timespec32 *ts asm("r1") = _ts;
+	register clockid_t clkid asm("r0") = _clkid;
+	register long ret asm ("r0");
+	register long nr asm("r7") = __NR_compat_clock_getres;
+
+	/* The checks below are required for ABI consistency with arm */
+	if ((_clkid >= MAX_CLOCKS) && (_ts == NULL))
 		return -EINVAL;
 
 	asm volatile(