From: Paolo 'Blaisorblade' Giarrusso <[email protected]>
The problems in this area came to light while fixing a compile failure with
GCC 4, in commit bcb01b8a67476e6f748086e626df8424cc27036d. I went comparing this
code with x86_64 frame construction (which we should ABI compatible with) and
resync'ed the code a bit.
It isn't yet perfect, because we don't yet save floating point context. But that
will come later.
Please give a critical eye, even because things currently have no reported
misbehaviour, and this code is complex enough.
CC: Andi Kleen <[email protected]>
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <[email protected]>
---
arch/um/sys-x86_64/signal.c | 19 ++++++++++++++++---
1 files changed, 16 insertions(+), 3 deletions(-)
diff --git a/arch/um/sys-x86_64/signal.c b/arch/um/sys-x86_64/signal.c
--- a/arch/um/sys-x86_64/signal.c
+++ b/arch/um/sys-x86_64/signal.c
@@ -164,6 +164,7 @@ struct rt_sigframe
#define round_down(m, n) (((m) / (n)) * (n))
+/* Taken from arch/x86_64/kernel/signal.c:setup_rt_frame(). */
int setup_signal_stack_si(unsigned long stack_top, int sig,
struct k_sigaction *ka, struct pt_regs * regs,
siginfo_t *info, sigset_t *set)
@@ -173,9 +174,21 @@ int setup_signal_stack_si(unsigned long
int err = 0;
struct task_struct *me = current;
- frame = (struct rt_sigframe __user *)
- round_down(stack_top - sizeof(struct rt_sigframe), 16) - 8;
- frame = (struct rt_sigframe *) ((unsigned long) frame - 128);
+ /* Leave space on the stack for the Red Zone, and for saving FP
+ * registers, even if this doesn't happen. We don't have a way to test
+ * used_math(), so we do that inconditionally.
+ *
+ * XXX: RED-PEN: currently, we're using a Red Zone also for any
+ * alternate stack set up by sigaltstack(), which x86-64 doesn't do
+ * (because there shouldn't be any code executing there). This could
+ * cause failures if user setup a too little alternate stack.*/
+
+ fp = (struct rt_sigframe *) round_down(stack_top - 128 -
+ sizeof(struct _fpstate), 16);
+
+ /* Now leave the space for the rest of signal frame. */
+ frame = (void __user *) round_down((unsigned long) fp -
+ sizeof(struct rt_sigframe), 16) - 8;
if (!access_ok(VERIFY_WRITE, fp, sizeof(struct _fpstate)))
goto out;
-
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