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Diffstat (limited to 'arch/x86/kernel/signal.c')
-rw-r--r--arch/x86/kernel/signal.c114
1 files changed, 93 insertions, 21 deletions
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index c07ff5ddbd47..548ddf7d6fd2 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -61,7 +61,38 @@
regs->seg = GET_SEG(seg) | 3; \
} while (0)
-int restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc)
+#ifdef CONFIG_X86_64
+/*
+ * If regs->ss will cause an IRET fault, change it. Otherwise leave it
+ * alone. Using this generally makes no sense unless
+ * user_64bit_mode(regs) would return true.
+ */
+static void force_valid_ss(struct pt_regs *regs)
+{
+ u32 ar;
+ asm volatile ("lar %[old_ss], %[ar]\n\t"
+ "jz 1f\n\t" /* If invalid: */
+ "xorl %[ar], %[ar]\n\t" /* set ar = 0 */
+ "1:"
+ : [ar] "=r" (ar)
+ : [old_ss] "rm" ((u16)regs->ss));
+
+ /*
+ * For a valid 64-bit user context, we need DPL 3, type
+ * read-write data or read-write exp-down data, and S and P
+ * set. We can't use VERW because VERW doesn't check the
+ * P bit.
+ */
+ ar &= AR_DPL_MASK | AR_S | AR_P | AR_TYPE_MASK;
+ if (ar != (AR_DPL3 | AR_S | AR_P | AR_TYPE_RWDATA) &&
+ ar != (AR_DPL3 | AR_S | AR_P | AR_TYPE_RWDATA_EXPDOWN))
+ regs->ss = __USER_DS;
+}
+#endif
+
+static int restore_sigcontext(struct pt_regs *regs,
+ struct sigcontext __user *sc,
+ unsigned long uc_flags)
{
unsigned long buf_val;
void __user *buf;
@@ -94,15 +125,18 @@ int restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc)
COPY(r15);
#endif /* CONFIG_X86_64 */
-#ifdef CONFIG_X86_32
COPY_SEG_CPL3(cs);
COPY_SEG_CPL3(ss);
-#else /* !CONFIG_X86_32 */
- /* Kernel saves and restores only the CS segment register on signals,
- * which is the bare minimum needed to allow mixed 32/64-bit code.
- * App's signal handler can save/restore other segments if needed. */
- COPY_SEG_CPL3(cs);
-#endif /* CONFIG_X86_32 */
+
+#ifdef CONFIG_X86_64
+ /*
+ * Fix up SS if needed for the benefit of old DOSEMU and
+ * CRIU.
+ */
+ if (unlikely(!(uc_flags & UC_STRICT_RESTORE_SS) &&
+ user_64bit_mode(regs)))
+ force_valid_ss(regs);
+#endif
get_user_ex(tmpflags, &sc->flags);
regs->flags = (regs->flags & ~FIX_EFLAGS) | (tmpflags & FIX_EFLAGS);
@@ -165,6 +199,7 @@ int setup_sigcontext(struct sigcontext __user *sc, void __user *fpstate,
put_user_ex(regs->cs, &sc->cs);
put_user_ex(0, &sc->gs);
put_user_ex(0, &sc->fs);
+ put_user_ex(regs->ss, &sc->ss);
#endif /* CONFIG_X86_32 */
put_user_ex(fpstate, &sc->fpstate);
@@ -403,6 +438,21 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,
return 0;
}
#else /* !CONFIG_X86_32 */
+static unsigned long frame_uc_flags(struct pt_regs *regs)
+{
+ unsigned long flags;
+
+ if (cpu_has_xsave)
+ flags = UC_FP_XSTATE | UC_SIGCONTEXT_SS;
+ else
+ flags = UC_SIGCONTEXT_SS;
+
+ if (likely(user_64bit_mode(regs)))
+ flags |= UC_STRICT_RESTORE_SS;
+
+ return flags;
+}
+
static int __setup_rt_frame(int sig, struct ksignal *ksig,
sigset_t *set, struct pt_regs *regs)
{
@@ -422,10 +472,7 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,
put_user_try {
/* Create the ucontext. */
- if (cpu_has_xsave)
- put_user_ex(UC_FP_XSTATE, &frame->uc.uc_flags);
- else
- put_user_ex(0, &frame->uc.uc_flags);
+ put_user_ex(frame_uc_flags(regs), &frame->uc.uc_flags);
put_user_ex(0, &frame->uc.uc_link);
save_altstack_ex(&frame->uc.uc_stack, regs->sp);
@@ -459,10 +506,28 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,
regs->sp = (unsigned long)frame;
- /* Set up the CS register to run signal handlers in 64-bit mode,
- even if the handler happens to be interrupting 32-bit code. */
+ /*
+ * Set up the CS and SS registers to run signal handlers in
+ * 64-bit mode, even if the handler happens to be interrupting
+ * 32-bit or 16-bit code.
+ *
+ * SS is subtle. In 64-bit mode, we don't need any particular
+ * SS descriptor, but we do need SS to be valid. It's possible
+ * that the old SS is entirely bogus -- this can happen if the
+ * signal we're trying to deliver is #GP or #SS caused by a bad
+ * SS value. We also have a compatbility issue here: DOSEMU
+ * relies on the contents of the SS register indicating the
+ * SS value at the time of the signal, even though that code in
+ * DOSEMU predates sigreturn's ability to restore SS. (DOSEMU
+ * avoids relying on sigreturn to restore SS; instead it uses
+ * a trampoline.) So we do our best: if the old SS was valid,
+ * we keep it. Otherwise we replace it.
+ */
regs->cs = __USER_CS;
+ if (unlikely(regs->ss != __USER_DS))
+ force_valid_ss(regs);
+
return 0;
}
#endif /* CONFIG_X86_32 */
@@ -489,10 +554,7 @@ static int x32_setup_rt_frame(struct ksignal *ksig,
put_user_try {
/* Create the ucontext. */
- if (cpu_has_xsave)
- put_user_ex(UC_FP_XSTATE, &frame->uc.uc_flags);
- else
- put_user_ex(0, &frame->uc.uc_flags);
+ put_user_ex(frame_uc_flags(regs), &frame->uc.uc_flags);
put_user_ex(0, &frame->uc.uc_link);
compat_save_altstack_ex(&frame->uc.uc_stack, regs->sp);
put_user_ex(0, &frame->uc.uc__pad0);
@@ -554,7 +616,11 @@ asmlinkage unsigned long sys_sigreturn(void)
set_current_blocked(&set);
- if (restore_sigcontext(regs, &frame->sc))
+ /*
+ * x86_32 has no uc_flags bits relevant to restore_sigcontext.
+ * Save a few cycles by skipping the __get_user.
+ */
+ if (restore_sigcontext(regs, &frame->sc, 0))
goto badframe;
return regs->ax;
@@ -570,16 +636,19 @@ asmlinkage long sys_rt_sigreturn(void)
struct pt_regs *regs = current_pt_regs();
struct rt_sigframe __user *frame;
sigset_t set;
+ unsigned long uc_flags;
frame = (struct rt_sigframe __user *)(regs->sp - sizeof(long));
if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
goto badframe;
if (__copy_from_user(&set, &frame->uc.uc_sigmask, sizeof(set)))
goto badframe;
+ if (__get_user(uc_flags, &frame->uc.uc_flags))
+ goto badframe;
set_current_blocked(&set);
- if (restore_sigcontext(regs, &frame->uc.uc_mcontext))
+ if (restore_sigcontext(regs, &frame->uc.uc_mcontext, uc_flags))
goto badframe;
if (restore_altstack(&frame->uc.uc_stack))
@@ -766,6 +835,7 @@ asmlinkage long sys32_x32_rt_sigreturn(void)
struct pt_regs *regs = current_pt_regs();
struct rt_sigframe_x32 __user *frame;
sigset_t set;
+ unsigned long uc_flags;
frame = (struct rt_sigframe_x32 __user *)(regs->sp - 8);
@@ -773,10 +843,12 @@ asmlinkage long sys32_x32_rt_sigreturn(void)
goto badframe;
if (__copy_from_user(&set, &frame->uc.uc_sigmask, sizeof(set)))
goto badframe;
+ if (__get_user(uc_flags, &frame->uc.uc_flags))
+ goto badframe;
set_current_blocked(&set);
- if (restore_sigcontext(regs, &frame->uc.uc_mcontext))
+ if (restore_sigcontext(regs, &frame->uc.uc_mcontext, uc_flags))
goto badframe;
if (compat_restore_altstack(&frame->uc.uc_stack))