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authorDave Hansen <dave.hansen@linux.intel.com>2017-10-18 10:21:07 -0700
committerIngo Molnar <mingo@kernel.org>2017-10-20 10:37:33 +0200
commitda20ab35180780e4a6eadc804544f1fa967f3567 (patch)
tree0c70b8daa761d4013d5bc8b3bb7f9091d7bca2cd /arch/x86/kernel/ldt.c
parentfc72ae40e30327aa24eb88a24b9c7058f938bd36 (diff)
x86/entry: Use SYSCALL_DEFINE() macros for sys_modify_ldt()
We do not have tracepoints for sys_modify_ldt() because we define it directly instead of using the normal SYSCALL_DEFINEx() macros. However, there is a reason sys_modify_ldt() does not use the macros: it has an 'int' return type instead of 'unsigned long'. This is a bug, but it's a bug cemented in the ABI. What does this mean? If we return -EINVAL from a function that returns 'int', we have 0x00000000ffffffea in %rax. But, if we return -EINVAL from a function returning 'unsigned long', we end up with 0xffffffffffffffea in %rax, which is wrong. To work around this and maintain the 'int' behavior while using the SYSCALL_DEFINEx() macros, so we add a cast to 'unsigned int' in both implementations of sys_modify_ldt(). Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Andy Lutomirski <luto@kernel.org> Reviewed-by: Brian Gerst <brgerst@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/20171018172107.1A79C532@viggo.jf.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/kernel/ldt.c')
-rw-r--r--arch/x86/kernel/ldt.c16
1 files changed, 13 insertions, 3 deletions
diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
index f0e64db18ac8..0402d44deb4d 100644
--- a/arch/x86/kernel/ldt.c
+++ b/arch/x86/kernel/ldt.c
@@ -12,6 +12,7 @@
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/smp.h>
+#include <linux/syscalls.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/uaccess.h>
@@ -294,8 +295,8 @@ out:
return error;
}
-asmlinkage int sys_modify_ldt(int func, void __user *ptr,
- unsigned long bytecount)
+SYSCALL_DEFINE3(modify_ldt, int , func , void __user * , ptr ,
+ unsigned long , bytecount)
{
int ret = -ENOSYS;
@@ -313,5 +314,14 @@ asmlinkage int sys_modify_ldt(int func, void __user *ptr,
ret = write_ldt(ptr, bytecount, 0);
break;
}
- return ret;
+ /*
+ * The SYSCALL_DEFINE() macros give us an 'unsigned long'
+ * return type, but tht ABI for sys_modify_ldt() expects
+ * 'int'. This cast gives us an int-sized value in %rax
+ * for the return code. The 'unsigned' is necessary so
+ * the compiler does not try to sign-extend the negative
+ * return codes into the high half of the register when
+ * taking the value from int->long.
+ */
+ return (unsigned int)ret;
}