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Diffstat (limited to 'arch/x86/include/asm/entry-common.h')
-rw-r--r--arch/x86/include/asm/entry-common.h16
1 files changed, 16 insertions, 0 deletions
diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h
index 2b87b191b3b8..14ebd2196569 100644
--- a/arch/x86/include/asm/entry-common.h
+++ b/arch/x86/include/asm/entry-common.h
@@ -2,6 +2,7 @@
#ifndef _ASM_X86_ENTRY_COMMON_H
#define _ASM_X86_ENTRY_COMMON_H
+#include <linux/randomize_kstack.h>
#include <linux/user-return-notifier.h>
#include <asm/nospec-branch.h>
@@ -70,6 +71,21 @@ static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
*/
current_thread_info()->status &= ~(TS_COMPAT | TS_I386_REGS_POKED);
#endif
+
+ /*
+ * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(),
+ * but not enough for x86 stack utilization comfort. To keep
+ * reasonable stack head room, reduce the maximum offset to 8 bits.
+ *
+ * The actual entropy will be further reduced by the compiler when
+ * applying stack alignment constraints (see cc_stack_align4/8 in
+ * arch/x86/Makefile), which will remove the 3 (x86_64) or 2 (ia32)
+ * low bits from any entropy chosen here.
+ *
+ * Therefore, final stack offset entropy will be 5 (x86_64) or
+ * 6 (ia32) bits.
+ */
+ choose_random_kstack_offset(rdtsc() & 0xFF);
}
#define arch_exit_to_user_mode_prepare arch_exit_to_user_mode_prepare