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authorLinus Torvalds <torvalds@linux-foundation.org>2020-05-17 11:08:29 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-05-17 11:08:29 -0700
commit43567139f5f3808cda4f61c956576f8a4f2232cb (patch)
treea878bdae763213bbde2d1deaab2c7a7f102d0d90
parent5a9ffb954a3933d7867f4341684a23e008d6839b (diff)
parenta9a3ed1eff3601b63aea4fb462d8b3b92c7c1e7e (diff)
downloadlinux-43567139f5f3808cda4f61c956576f8a4f2232cb.tar.gz
Merge tag 'x86_urgent_for_v5.7-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 fix from Borislav Petkov: "A single fix for early boot crashes of kernels built with gcc10 and stack protector enabled" * tag 'x86_urgent_for_v5.7-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86: Fix early boot crash on gcc-10, third try
-rw-r--r--arch/x86/include/asm/stackprotector.h7
-rw-r--r--arch/x86/kernel/smpboot.c8
-rw-r--r--arch/x86/xen/smp_pv.c1
-rw-r--r--include/linux/compiler.h6
-rw-r--r--init/main.c2
5 files changed, 23 insertions, 1 deletions
diff --git a/arch/x86/include/asm/stackprotector.h b/arch/x86/include/asm/stackprotector.h
index 91e29b6a86a5..9804a7957f4e 100644
--- a/arch/x86/include/asm/stackprotector.h
+++ b/arch/x86/include/asm/stackprotector.h
@@ -55,8 +55,13 @@
/*
* Initialize the stackprotector canary value.
*
- * NOTE: this must only be called from functions that never return,
+ * NOTE: this must only be called from functions that never return
* and it must always be inlined.
+ *
+ * In addition, it should be called from a compilation unit for which
+ * stack protector is disabled. Alternatively, the caller should not end
+ * with a function call which gets tail-call optimized as that would
+ * lead to checking a modified canary value.
*/
static __always_inline void boot_init_stack_canary(void)
{
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 8c89e4d9ad28..2f24c334a938 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -266,6 +266,14 @@ static void notrace start_secondary(void *unused)
wmb();
cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
+
+ /*
+ * Prevent tail call to cpu_startup_entry() because the stack protector
+ * guard has been changed a couple of function calls up, in
+ * boot_init_stack_canary() and must not be checked before tail calling
+ * another function.
+ */
+ prevent_tail_call_optimization();
}
/**
diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
index 8fb8a50a28b4..f2adb63b2d7c 100644
--- a/arch/x86/xen/smp_pv.c
+++ b/arch/x86/xen/smp_pv.c
@@ -93,6 +93,7 @@ asmlinkage __visible void cpu_bringup_and_idle(void)
cpu_bringup();
boot_init_stack_canary();
cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
+ prevent_tail_call_optimization();
}
void xen_smp_intr_free_pv(unsigned int cpu)
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 034b0a644efc..448c91bf543b 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -356,4 +356,10 @@ static inline void *offset_to_ptr(const int *off)
/* &a[0] degrades to a pointer: a different type from an array */
#define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
+/*
+ * This is needed in functions which generate the stack canary, see
+ * arch/x86/kernel/smpboot.c::start_secondary() for an example.
+ */
+#define prevent_tail_call_optimization() mb()
+
#endif /* __LINUX_COMPILER_H */
diff --git a/init/main.c b/init/main.c
index 5803ecb411ab..03371976d387 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1038,6 +1038,8 @@ asmlinkage __visible void __init start_kernel(void)
/* Do the rest non-__init'ed, we're now alive */
arch_call_rest_init();
+
+ prevent_tail_call_optimization();
}
/* Call all constructor functions linked into the kernel. */