[PATCH] x86: limit the fs segment to the pointer size

[Masahiro Yamada]

The fs segment is only used to get the global data pointer.
If it is accessed beyond sizeof(new_gd->arch.gd_addr), it is a bug.

To specify the byte-granule limit size, drop the G bit, so the
flag field is 0x8093 instead of 0xc093, and set the limit field
to sizeof(new_gd->arch.gd_addr) - 1.

Signed-off-by: Masahiro Yamada <masahiroy at kernel.org>
---

 arch/x86/cpu/i386/cpu.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/cpu/i386/cpu.c b/arch/x86/cpu/i386/cpu.c
index 2b27617ca3a4..72fefdd3adca 100644
--- a/arch/x86/cpu/i386/cpu.c
+++ b/arch/x86/cpu/i386/cpu.c
@@ -137,8 +137,9 @@ void arch_setup_gd(gd_t *new_gd)
 
 	/* FS: data, read/write, 4 GB, base (Global Data Pointer) */
 	new_gd->arch.gd_addr = new_gd;
-	gdt_addr[X86_GDT_ENTRY_32BIT_FS] = GDT_ENTRY(0xc093,
-		     (ulong)&new_gd->arch.gd_addr, 0xfffff);
+	gdt_addr[X86_GDT_ENTRY_32BIT_FS] = GDT_ENTRY(0x8093,
+					(ulong)&new_gd->arch.gd_addr,
+					sizeof(new_gd->arch.gd_addr) - 1);
 
 	/* 16-bit CS: code, read/execute, 64 kB, base 0 */
 	gdt_addr[X86_GDT_ENTRY_16BIT_CS] = GDT_ENTRY(0x009b, 0, 0x0ffff);
-- 
2.17.1