[gentoo-commits] proj/linux-patches:5.4 commit in: /

[Mike Pagano]

commit:     69d12816ea9f46070999271a2932ee9ff8954950
Author:     Mike Pagano <mpagano <AT> gentoo <DOT> org>
AuthorDate: Sat May  9 22:11:36 2020 +0000
Commit:     Mike Pagano <mpagano <AT> gentoo <DOT> org>
CommitDate: Sat May  9 22:11:36 2020 +0000
URL:        https://gitweb.gentoo.org/proj/linux-patches.git/commit/?id=69d12816

x86: Fix early boot crash on gcc-10

Bug: https://bugs.gentoo.org/721734

Signed-off-by: Mike Pagano <mpagano <AT> gentoo.org>

 0000_README                                |   4 +
 1700_x86-gcc-10-early-boot-crash-fix.patch | 131 +++++++++++++++++++++++++++++
 2 files changed, 135 insertions(+)

diff --git a/0000_README b/0000_README
index c1ac1b1..ea8edd3 100644
--- a/0000_README
+++ b/0000_README
@@ -207,6 +207,10 @@ Patch:  1510_fs-enable-link-security-restrictions-by-default.patch
 From:   http://sources.debian.net/src/linux/3.16.7-ckt4-3/debian/patches/debian/fs-enable-link-security-restrictions-by-default.patch/
 Desc:   Enable link security restrictions by default.
 
+Patch:  1700_x86-gcc-10-early-boot-crash-fix.patch
+From:   https://https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/patch/?id=f670269a42bfdd2c83a1118cc3d1b475547eac22
+Desc:   x86: Fix early boot crash on gcc-10
+
 Patch:  2000_BT-Check-key-sizes-only-if-Secure-Simple-Pairing-enabled.patch
 From:   https://lore.kernel.org/linux-bluetooth/20190522070540.48895-1-marcel@××××××××.org/raw
 Desc:   Bluetooth: Check key sizes only when Secure Simple Pairing is enabled. See bug #686758

diff --git a/1700_x86-gcc-10-early-boot-crash-fix.patch b/1700_x86-gcc-10-early-boot-crash-fix.patch
new file mode 100644
index 0000000..8cdf651
--- /dev/null
+++ b/1700_x86-gcc-10-early-boot-crash-fix.patch
@@ -0,0 +1,131 @@
+From f670269a42bfdd2c83a1118cc3d1b475547eac22 Mon Sep 17 00:00:00 2001
+From: Borislav Petkov <bp@××××.de>
+Date: Wed, 22 Apr 2020 18:11:30 +0200
+Subject: 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@g.o>
+Signed-off-by: Borislav Petkov <bp@××××.de>
+Reviewed-by: Nick Desaulniers <ndesaulniers@××××××.com>
+Reviewed-by: Kees Cook <keescook@××××××××.org>
+Link: https://lkml.kernel.org/r/20200314164451.346497-1-slyfox@g.o
+---
+ 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 fe3ab9632f3b..4f275ac7830b 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..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 */
+-- 
+cgit 1.2-0.3.lf.el7
+