linux-kernel - [patch 4/5] x86/vdso/32: Use 32bit syscall fallback

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Date:   Sun, 28 Jul 2019 15:12:55 +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 4/5] 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.

Reported-by: Sean Christopherson <sean.j.christopherson@...el.com>
Reported-by: Paul Bolle <pebolle@...cali.nl>
Suggested-by: Andy Lutomirski <luto@...nel.org>
Fixes: 7ac870747988 ("x86/vdso: Switch to generic vDSO implementation")
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 arch/x86/include/asm/vdso/gettimeofday.h |   36 +++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

--- 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 _cl
 
 #else
 
+#define VDSO_HAS_32BIT_FALLBACK	1
+
 static __always_inline
 long clock_gettime_fallback(clockid_t _clkid, struct __kernel_timespec *_ts)
 {
@@ -114,6 +116,23 @@ long clock_gettime_fallback(clockid_t _c
 }
 
 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)
 {
@@ -146,6 +165,23 @@ clock_getres_fallback(clockid_t _clkid,
 		: "edx");
 
 	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