From a0f7085f6a63f19f83f2644ce2da49a8d3cf7c0f Mon Sep 17 00:00:00 2001
From: Jinjie Ruan <ruanjinjie@huawei.com>
Date: Sat, 20 Jul 2024 22:40:58 +0800
Subject: [PATCH] LoongArch: Add RANDOMIZE_KSTACK_OFFSET support
Add support of kernel stack offset randomization while handling syscall,
the offset is defaultly limited by KSTACK_OFFSET_MAX().
In order to avoid triggering stack canaries (due to __builtin_alloca())
and slowing down the entry path, use __no_stack_protector attribute to
disable stack protector for do_syscall() at function level.
With this patch, the REPORT_STACK test show that:
`loongarch64 bits of stack entropy: 7`
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
---
arch/loongarch/Kconfig | 1 +
arch/loongarch/kernel/syscall.c | 22 +++++++++++++++++++++-
2 files changed, 22 insertions(+), 1 deletion(-)
diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index ddc042895d011..fcf6451b4e384 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -106,6 +106,7 @@ config LOONGARCH
select HAVE_ARCH_KFENCE
select HAVE_ARCH_KGDB if PERF_EVENTS
select HAVE_ARCH_MMAP_RND_BITS if MMU
+ select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
select HAVE_ARCH_SECCOMP
select HAVE_ARCH_SECCOMP_FILTER
select HAVE_ARCH_TRACEHOOK
diff --git a/arch/loongarch/kernel/syscall.c b/arch/loongarch/kernel/syscall.c
index ec17cd5163b7c..ba5d0930a74f7 100644
--- a/arch/loongarch/kernel/syscall.c
+++ b/arch/loongarch/kernel/syscall.c
@@ -9,11 +9,14 @@
#include <linux/entry-common.h>
#include <linux/errno.h>
#include <linux/linkage.h>
+#include <linux/objtool.h>
+#include <linux/randomize_kstack.h>
#include <linux/syscalls.h>
#include <linux/unistd.h>
#include <asm/asm.h>
#include <asm/exception.h>
+#include <asm/loongarch.h>
#include <asm/signal.h>
#include <asm/switch_to.h>
#include <asm-generic/syscalls.h>
@@ -39,7 +42,7 @@ void *sys_call_table[__NR_syscalls] = {
typedef long (*sys_call_fn)(unsigned long, unsigned long,
unsigned long, unsigned long, unsigned long, unsigned long);
-void noinstr do_syscall(struct pt_regs *regs)
+void noinstr __no_stack_protector do_syscall(struct pt_regs *regs)
{
unsigned long nr;
sys_call_fn syscall_fn;
@@ -55,11 +58,28 @@ void noinstr do_syscall(struct pt_regs *regs)
nr = syscall_enter_from_user_mode(regs, nr);
+ add_random_kstack_offset();
+
if (nr < NR_syscalls) {
syscall_fn = sys_call_table[nr];
regs->regs[4] = syscall_fn(regs->orig_a0, regs->regs[5], regs->regs[6],
regs->regs[7], regs->regs[8], regs->regs[9]);
}
+ /*
+ * This value will get limited by KSTACK_OFFSET_MAX(), which is 10
+ * bits. The actual entropy will be further reduced by the compiler
+ * when applying stack alignment constraints: 16-bytes (i.e. 4-bits)
+ * aligned, which will remove the 4 low bits from any entropy chosen
+ * here.
+ *
+ * The resulting 6 bits of entropy is seen in SP[9:4].
+ */
+ choose_random_kstack_offset(drdtime());
+
syscall_exit_to_user_mode(regs);
}
+
+#ifdef CONFIG_RANDOMIZE_KSTACK_OFFSET
+STACK_FRAME_NON_STANDARD(do_syscall);
+#endif
--
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