x86/ia32: Fix ia32_restore_sigcontext() AC leak

BugLink: https://bugs.launchpad.net/bugs/1837517
[ Upstream commit 67a0514afdbb8b2fc70b771b8c77661a9cb9d3a9 ]

Objtool spotted that we call native_load_gs_index() with AC set.
Re-arrange the code to avoid that.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c
index 321fe5f5d0e96f8ed3f4962dbf982bc60551cf0e..4d5fcd47ab75a4e2815f2ed381b9356b3c18e7d1 100644 (file)
--- a/arch/x86/ia32/ia32_signal.c
+++ b/arch/x86/ia32/ia32_signal.c
@@ -61,9 +61,8 @@
 } while (0)
 
 #define RELOAD_SEG(seg)                {               \
-       unsigned int pre = GET_SEG(seg);        \
+       unsigned int pre = (seg) | 3;           \
        unsigned int cur = get_user_seg(seg);   \
-       pre |= 3;                               \
        if (pre != cur)                         \
                set_user_seg(seg, pre);         \
 }
@@ -72,6 +71,7 @@ static int ia32_restore_sigcontext(struct pt_regs *regs,
                                   struct sigcontext_32 __user *sc)
 {
        unsigned int tmpflags, err = 0;
+       u16 gs, fs, es, ds;
        void __user *buf;
        u32 tmp;
 
@@ -79,16 +79,10 @@ static int ia32_restore_sigcontext(struct pt_regs *regs,
        current->restart_block.fn = do_no_restart_syscall;
 
        get_user_try {
-               /*
-                * Reload fs and gs if they have changed in the signal
-                * handler.  This does not handle long fs/gs base changes in
-                * the handler, but does not clobber them at least in the
-                * normal case.
-                */
-               RELOAD_SEG(gs);
-               RELOAD_SEG(fs);
-               RELOAD_SEG(ds);
-               RELOAD_SEG(es);
+               gs = GET_SEG(gs);
+               fs = GET_SEG(fs);
+               ds = GET_SEG(ds);
+               es = GET_SEG(es);
 
                COPY(di); COPY(si); COPY(bp); COPY(sp); COPY(bx);
                COPY(dx); COPY(cx); COPY(ip); COPY(ax);
@@ -106,6 +100,17 @@ static int ia32_restore_sigcontext(struct pt_regs *regs,
                buf = compat_ptr(tmp);
        } get_user_catch(err);
 
+       /*
+        * Reload fs and gs if they have changed in the signal
+        * handler.  This does not handle long fs/gs base changes in
+        * the handler, but does not clobber them at least in the
+        * normal case.
+        */
+       RELOAD_SEG(gs);
+       RELOAD_SEG(fs);
+       RELOAD_SEG(ds);
+       RELOAD_SEG(es);
+
        err |= fpu__restore_sig(buf, 1);
 
        force_iret();