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Commit da20ab35 authored by Dave Hansen's avatar Dave Hansen Committed by Ingo Molnar
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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: default avatarDave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: default avatarAndy Lutomirski <luto@kernel.org>
Reviewed-by: default avatarBrian 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: default avatarIngo Molnar <mingo@kernel.org>
parent fc72ae40

arch/x86/include/asm/syscalls.h

+1 −1
Original line number Diff line number Diff line
@@ -21,7 +21,7 @@ asmlinkage long sys_ioperm(unsigned long, unsigned long, int); 
asmlinkage long sys_iopl(unsigned int);



/* kernel/ldt.c */

asmlinkage int sys_modify_ldt(int, void __user *, unsigned long);

asmlinkage long sys_modify_ldt(int, void __user *, unsigned long);



/* kernel/signal.c */

asmlinkage long sys_rt_sigreturn(void);

arch/x86/kernel/ldt.c

+13 −3
Original line number Diff line number Diff line
@@ -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 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode) 
	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;

}

arch/x86/um/ldt.c

+5 −2
Original line number Diff line number Diff line
@@ -6,6 +6,7 @@ 
#include <linux/mm.h>

#include <linux/sched.h>

#include <linux/slab.h>

#include <linux/syscalls.h>

#include <linux/uaccess.h>

#include <asm/unistd.h>

#include <os.h>
@@ -369,7 +370,9 @@ void free_ldt(struct mm_context *mm) 
	mm->arch.ldt.entry_count = 0;

}



int sys_modify_ldt(int func, void __user *ptr, unsigned long bytecount)

SYSCALL_DEFINE3(modify_ldt, int , func , void __user * , ptr ,

		unsigned long , bytecount)

{

	return do_modify_ldt_skas(func, ptr, bytecount);

	/* See non-um modify_ldt() for why we do this cast */

	return (unsigned int)do_modify_ldt_skas(func, ptr, bytecount);

}