diff options
Diffstat (limited to 'libre/linux-libre-pae/0005-x86-Fix-early-boot-crash-on-gcc-10-next-try.patch')
| -rw-r--r-- | libre/linux-libre-pae/0005-x86-Fix-early-boot-crash-on-gcc-10-next-try.patch | 131 |
1 files changed, 131 insertions, 0 deletions
diff --git a/libre/linux-libre-pae/0005-x86-Fix-early-boot-crash-on-gcc-10-next-try.patch b/libre/linux-libre-pae/0005-x86-Fix-early-boot-crash-on-gcc-10-next-try.patch new file mode 100644 index 000000000..78505e790 --- /dev/null +++ b/libre/linux-libre-pae/0005-x86-Fix-early-boot-crash-on-gcc-10-next-try.patch @@ -0,0 +1,131 @@ +From 53e90d763b7fe8bec6a0c86b6813131cd8e25026 Mon Sep 17 00:00:00 2001 +From: Borislav Petkov <bp@suse.de> +Date: Wed, 22 Apr 2020 18:11:30 +0200 +Subject: [PATCH 5/5] x86: Fix early boot crash on gcc-10, next try +MIME-Version: 1.0 +Content-Type: text/plain; charset=UTF-8 +Content-Transfer-Encoding: 8bit + +... or the odyssey of trying to disable the stack protector for the +function which generates the stack canary value. + +The whole story started with Sergei reporting a boot crash with a kernel +built with gcc-10: + + Kernel panic — not syncing: stack-protector: Kernel stack is corrupted in: start_secondary + CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.6.0-rc5—00235—gfffb08b37df9 #139 + Hardware name: Gigabyte Technology Co., Ltd. To be filled by O.E.M./H77M—D3H, BIOS F12 11/14/2013 + Call Trace: + dump_stack + panic + ? start_secondary + __stack_chk_fail + start_secondary + secondary_startup_64 + -—-[ end Kernel panic — not syncing: stack—protector: Kernel stack is corrupted in: start_secondary + +This happens because gcc-10 tail-call optimizes the last function call +in start_secondary() - cpu_startup_entry() - and thus emits a stack +canary check which fails because the canary value changes after the +boot_init_stack_canary() call. + +To fix that, the initial attempt was to mark the one function which +generates the stack canary with: + + __attribute__((optimize("-fno-stack-protector"))) ... start_secondary(void *unused) + +however, using the optimize attribute doesn't work cumulatively +as the attribute does not add to but rather replaces previously +supplied optimization options - roughly all -fxxx options. + +The key one among them being -fno-omit-frame-pointer and thus leading to +not present frame pointer - frame pointer which the kernel needs. + +The next attempt to prevent compilers from tail-call optimizing +the last function call cpu_startup_entry(), shy of carving out +start_secondary() into a separate compilation unit and building it with +-fno-stack-protector, is this one. + +The current solution is short and sweet, and reportedly, is supported by +both compilers so let's see how far we'll get this time. + +Reported-by: Sergei Trofimovich <slyfox@gentoo.org> +Signed-off-by: Borislav Petkov <bp@suse.de> +Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> +Reviewed-by: Kees Cook <keescook@chromium.org> +Link: https://lkml.kernel.org/r/20200314164451.346497-1-slyfox@gentoo.org +--- + arch/x86/include/asm/stackprotector.h | 7 ++++++- + arch/x86/kernel/smpboot.c | 8 ++++++++ + arch/x86/xen/smp_pv.c | 1 + + include/linux/compiler.h | 6 ++++++ + 4 files changed, 21 insertions(+), 1 deletion(-) + +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 69881b2d446c..9674321ce3a3 100644 +--- a/arch/x86/kernel/smpboot.c ++++ b/arch/x86/kernel/smpboot.c +@@ -262,6 +262,14 @@ 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 802ee5bba66c..0cebe5db691d 100644 +--- a/arch/x86/xen/smp_pv.c ++++ b/arch/x86/xen/smp_pv.c +@@ -92,6 +92,7 @@ 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..732754d96039 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() asm("") ++ + #endif /* __LINUX_COMPILER_H */ +-- +2.26.2 + |