[PATCH 05/12] __wr_after_init: x86_64: debug writes

[Igor Stoppa]

After each write operation, confirm that it was successful, otherwise
generate a warning.

Signed-off-by: Igor Stoppa <igor.stoppa@xxxxxxxxxx>

CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
CC: Nadav Amit <nadav.amit@xxxxxxxxx>
CC: Matthew Wilcox <willy@xxxxxxxxxxxxx>
CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CC: Kees Cook <keescook@xxxxxxxxxxxx>
CC: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
CC: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
CC: linux-integrity@xxxxxxxxxxxxxxx
CC: kernel-hardening@xxxxxxxxxxxxxxxxxx
CC: linux-mm@xxxxxxxxx
CC: linux-kernel@xxxxxxxxxxxxxxx
---
 arch/x86/mm/prmem.c | 9 ++++++++-
 mm/Kconfig.debug    | 8 ++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/prmem.c b/arch/x86/mm/prmem.c
index fc367551e736..9d98525c687a 100644
--- a/arch/x86/mm/prmem.c
+++ b/arch/x86/mm/prmem.c
@@ -60,7 +60,14 @@ void *__wr_op(unsigned long dst, unsigned long src, __kernel_size_t len,
 		copy_to_user((void __user *)wr_poking_addr, (void *)src, len);
 	else if (op == WR_MEMSET)
 		memset_user((void __user *)wr_poking_addr, (u8)src, len);
-
+#ifdef CONFIG_DEBUG_PRMEM
+	if (op == WR_MEMCPY)
+		VM_WARN_ONCE(memcmp((void *)dst, (void *)src, len),
+			     "Failed wr_memcpy()");
+	else if (op == WR_MEMSET)
+		VM_WARN_ONCE(memtst((void *)dst, (u8)src, len),
+			     "Failed wr_memset()");
+#endif
 	unuse_temporary_mm(prev);
 	local_irq_enable();
 	return (void *)dst;
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 9a7b8b049d04..b10305cfac3c 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -94,3 +94,11 @@ config DEBUG_RODATA_TEST
     depends on STRICT_KERNEL_RWX
     ---help---
       This option enables a testcase for the setting rodata read-only.
+
+config DEBUG_PRMEM
+    bool "Verify each write rare operation."
+    depends on PRMEM
+    default n
+    help
+      After any write rare operation, compares the data written with the
+      value provided by the caller.
-- 
2.19.1