linux-kernel - [tip:timers/urgent] x86/vdso/32: Use 32bit syscall fallback

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Message-ID: <tip-d2f5d3fa26196183adb44a413c44caa9872275b4@git.kernel.org>
Date:   Tue, 30 Jul 2019 15:21:24 -0700
From:   tip-bot for Thomas Gleixner <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     luto@...nel.org, mingo@...nel.org, sean.j.christopherson@...el.com,
        tglx@...utronix.de, vincenzo.frascino@....com, pebolle@...cali.nl,
        linux-kernel@...r.kernel.org, hpa@...or.com
Subject: [tip:timers/urgent] x86/vdso/32: Use 32bit syscall fallback

Commit-ID:  d2f5d3fa26196183adb44a413c44caa9872275b4
Gitweb:     https://git.kernel.org/tip/d2f5d3fa26196183adb44a413c44caa9872275b4
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Sun, 28 Jul 2019 15:12:55 +0200
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Wed, 31 Jul 2019 00:09:10 +0200

x86/vdso/32: Use 32bit syscall 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.

Fixes: 7ac870747988 ("x86/vdso: Switch to generic vDSO implementation")
Reported-by: Sean Christopherson <sean.j.christopherson@...el.com>
Reported-by: Paul Bolle <pebolle@...cali.nl>
Suggested-by: Andy Lutomirski <luto@...nel.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@....com>
Reviewed-by: Andy Lutomirski <luto@...nel.org>
Link: https://lkml.kernel.org/r/20190728131648.879156507@linutronix.de

---
 arch/x86/include/asm/vdso/gettimeofday.h | 36 ++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/arch/x86/include/asm/vdso/gettimeofday.h b/arch/x86/include/asm/vdso/gettimeofday.h
index ae91429129a6..ba71a63cdac4 100644
--- a/arch/x86/include/asm/vdso/gettimeofday.h
+++ b/arch/x86/include/asm/vdso/gettimeofday.h
@@ -96,6 +96,8 @@ long clock_getres_fallback(clockid_t _clkid, struct __kernel_timespec *_ts)
 
 #else
 
+#define VDSO_HAS_32BIT_FALLBACK	1
+
 static __always_inline
 long clock_gettime_fallback(clockid_t _clkid, struct __kernel_timespec *_ts)
 {
@@ -113,6 +115,23 @@ long clock_gettime_fallback(clockid_t _clkid, struct __kernel_timespec *_ts)
 	return ret;
 }
 
+static __always_inline
+long clock_gettime32_fallback(clockid_t _clkid, struct old_timespec32 *_ts)
+{
+	long ret;
+
+	asm (
+		"mov %%ebx, %%edx \n"
+		"mov %[clock], %%ebx \n"
+		"call __kernel_vsyscall \n"
+		"mov %%edx, %%ebx \n"
+		: "=a" (ret), "=m" (*_ts)
+		: "0" (__NR_clock_gettime), [clock] "g" (_clkid), "c" (_ts)
+		: "edx");
+
+	return ret;
+}
+
 static __always_inline
 long gettimeofday_fallback(struct __kernel_old_timeval *_tv,
 			   struct timezone *_tz)
@@ -148,6 +167,23 @@ clock_getres_fallback(clockid_t _clkid, struct __kernel_timespec *_ts)
 	return ret;
 }
 
+static __always_inline
+long clock_getres32_fallback(clockid_t _clkid, struct old_timespec32 *_ts)
+{
+	long ret;
+
+	asm (
+		"mov %%ebx, %%edx \n"
+		"mov %[clock], %%ebx \n"
+		"call __kernel_vsyscall \n"
+		"mov %%edx, %%ebx \n"
+		: "=a" (ret), "=m" (*_ts)
+		: "0" (__NR_clock_getres), [clock] "g" (_clkid), "c" (_ts)
+		: "edx");
+
+	return ret;
+}
+
 #endif
 
 #ifdef CONFIG_PARAVIRT_CLOCK