Disable CPU speculation-related misfeatures which are in
fact vulnerabilities causing data leaks:
- Speculative Store Bypass
- Indirect Branch Speculation
- Flush L1D Cache on context switch out of the task
For further information see the kernel documentation:
Documentation/userspace-api/spec_ctrl.rst
Signed-off-by: Guido Trentalancia <gu...@trentalancia.com>
---
common/init.c | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)
diff -pru a/common/init.c b/common/init.c
--- a/common/init.c 2024-05-15 12:33:38.000000000 +0200
+++ b/common/init.c 2025-06-27 12:35:33.543235132 +0200
@@ -29,6 +29,10 @@
#include <config.h>
+#if defined(__linux__)
+# include <sys/prctl.h>
+#endif
+
#ifdef HAVE_W32_SYSTEM
# if _WIN32_WINNT < 0x0600
# define _WIN32_WINNT 0x0600 /* Required for SetProcessDEPPolicy. */
@@ -131,6 +135,29 @@ writestring_via_estream (int mode, const
void
early_system_init (void)
{
+#if defined(__linux__)
+
+/* Disable CPU speculation-related misfeatures which are in
+ * fact vulnerabilities causing data leaks: see the kernel
+ * documentation: Documentation/userspace-api/spec_ctrl.rst
+ *
+ * - Speculative Store Bypass
+ * - Indirect Branch Speculation
+ * - Flush L1D Cache on context switch out of the task
+ */
+#ifdef PR_SPEC_STORE_BYPASS
+ prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_FORCE_DISABLE,
0, 0);
+#endif
+
+#ifdef PR_SPEC_INDIRECT_BRANCH
+ prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH,
PR_SPEC_FORCE_DISABLE, 0, 0);
+#endif
+
+#ifdef PR_SPEC_L1D_FLUSH
+ prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_L1D_FLUSH, PR_SPEC_FORCE_DISABLE, 0,
0);
+#endif
+
+#endif /* __linux__ */
}
On Mon, 26/05/2025 at 16.46 +0200, Werner Koch wrote:
> Hi!
>
> On Mon, 26 May 2025 14:00, Guido Trentalancia said:
> > Disable CPU speculation-related misfeatures which are in
> > fact vulnerabilities causing data leaks:
>
> If that is a misfeature it needs to be fixed at the pläce where it
> was
> introduced and not just in a single binary. If this code is really
> needed it would first of all be useful in Libgcrypt only then then
> you
> should put it into gnupg/common/init.c:early_system_init.
>
> Specific Linux code is in general not a good idea, if that is
> required,
> please write a proper configure test for this feature and use a
> dedicated macro. A more detailed explanation of the pro and cons
> would
> also be appreciated.
>
>
>
> Shalom-Salam,
>
> Werner
>
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