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-rw-r--r--arch/x86_64/kernel/signal.c17
1 files changed, 17 insertions, 0 deletions
diff --git a/arch/x86_64/kernel/signal.c b/arch/x86_64/kernel/signal.c
index d642fbf..5876df1 100644
--- a/arch/x86_64/kernel/signal.c
+++ b/arch/x86_64/kernel/signal.c
@@ -110,6 +110,15 @@ restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc, unsigned
COPY(r14);
COPY(r15);
+ /* 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. */
+ {
+ unsigned cs;
+ err |= __get_user(cs, &sc->cs);
+ regs->cs = cs | 3; /* Force into user mode */
+ }
+
{
unsigned int tmpflags;
err |= __get_user(tmpflags, &sc->eflags);
@@ -187,6 +196,7 @@ setup_sigcontext(struct sigcontext __user *sc, struct pt_regs *regs, unsigned lo
{
int err = 0;
+ err |= __put_user(regs->cs, &sc->cs);
err |= __put_user(0, &sc->gs);
err |= __put_user(0, &sc->fs);
@@ -318,7 +328,14 @@ static int setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
regs->rsp = (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. */
+ regs->cs = __USER_CS;
+
+ /* This, by contrast, has nothing to do with segment registers -
+ see include/asm-x86_64/uaccess.h for details. */
set_fs(USER_DS);
+
regs->eflags &= ~TF_MASK;
if (test_thread_flag(TIF_SINGLESTEP))
ptrace_notify(SIGTRAP);
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