Date: Saturday, May 9, 2020 @ 19:59:23 Author: heftig Revision: 382974
5.4.39-3: more GCC 10 fixes Added: linux-lts/trunk/0002-Makefile-disallow-data-races-on-gcc-10-as-well.patch linux-lts/trunk/0003-x86-Fix-early-boot-crash-on-gcc-10-next-try.patch Modified: linux-lts/trunk/0001-gcc-common.h-Update-for-GCC-10.patch linux-lts/trunk/PKGBUILD -----------------------------------------------------------+ 0001-gcc-common.h-Update-for-GCC-10.patch | 2 0002-Makefile-disallow-data-races-on-gcc-10-as-well.patch | 32 ++ 0003-x86-Fix-early-boot-crash-on-gcc-10-next-try.patch | 131 ++++++++++++ PKGBUILD | 8 4 files changed, 170 insertions(+), 3 deletions(-) Modified: 0001-gcc-common.h-Update-for-GCC-10.patch =================================================================== --- 0001-gcc-common.h-Update-for-GCC-10.patch 2020-05-09 19:59:19 UTC (rev 382973) +++ 0001-gcc-common.h-Update-for-GCC-10.patch 2020-05-09 19:59:23 UTC (rev 382974) @@ -2,7 +2,7 @@ From: =?UTF-8?q?Fr=C3=A9d=C3=A9ric=20Pierret=20=28fepitre=29?= <frederic.pier...@qubes-os.org> Date: Tue, 7 Apr 2020 13:32:59 +0200 -Subject: [PATCH] gcc-common.h: Update for GCC 10 +Subject: [PATCH 1/3] gcc-common.h: Update for GCC 10 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Added: 0002-Makefile-disallow-data-races-on-gcc-10-as-well.patch =================================================================== --- 0002-Makefile-disallow-data-races-on-gcc-10-as-well.patch (rev 0) +++ 0002-Makefile-disallow-data-races-on-gcc-10-as-well.patch 2020-05-09 19:59:23 UTC (rev 382974) @@ -0,0 +1,32 @@ +From 6a183a41a1945cb79660a78536182ce9c2568291 Mon Sep 17 00:00:00 2001 +From: Sergei Trofimovich <sly...@gentoo.org> +Date: Tue, 17 Mar 2020 00:07:18 +0000 +Subject: [PATCH 2/3] Makefile: disallow data races on gcc-10 as well + +gcc-10 will rename --param=allow-store-data-races=0 +to -fno-allow-store-data-races. + +The flag change happened at https://gcc.gnu.org/PR92046. + +Signed-off-by: Sergei Trofimovich <sly...@gentoo.org> +Acked-by: Jiri Kosina <jkos...@suse.cz> +Signed-off-by: Masahiro Yamada <masahi...@kernel.org> +--- + Makefile | 1 + + 1 file changed, 1 insertion(+) + +diff --git a/Makefile b/Makefile +index ff2b90ddc9bc..c8dc1357079b 100644 +--- a/Makefile ++++ b/Makefile +@@ -713,6 +713,7 @@ endif + + # Tell gcc to never replace conditional load with a non-conditional one + KBUILD_CFLAGS += $(call cc-option,--param=allow-store-data-races=0) ++KBUILD_CFLAGS += $(call cc-option,-fno-allow-store-data-races) + + include scripts/Makefile.kcov + include scripts/Makefile.gcc-plugins +-- +2.26.2 + Added: 0003-x86-Fix-early-boot-crash-on-gcc-10-next-try.patch =================================================================== --- 0003-x86-Fix-early-boot-crash-on-gcc-10-next-try.patch (rev 0) +++ 0003-x86-Fix-early-boot-crash-on-gcc-10-next-try.patch 2020-05-09 19:59:23 UTC (rev 382974) @@ -0,0 +1,131 @@ +From 2f18ace75890ccd9681f210efdb58662db0cb4c4 Mon Sep 17 00:00:00 2001 +From: Borislav Petkov <b...@suse.de> +Date: Wed, 22 Apr 2020 18:11:30 +0200 +Subject: [PATCH 3/3] 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 <sly...@gentoo.org> +Signed-off-by: Borislav Petkov <b...@suse.de> +Reviewed-by: Nick Desaulniers <ndesaulni...@google.com> +Reviewed-by: Kees Cook <keesc...@chromium.org> +Link: https://lkml.kernel.org/r/20200314164451.346497-1-sly...@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 + Modified: PKGBUILD =================================================================== --- PKGBUILD 2020-05-09 19:59:19 UTC (rev 382973) +++ PKGBUILD 2020-05-09 19:59:23 UTC (rev 382974) @@ -2,7 +2,7 @@ pkgbase=linux-lts pkgver=5.4.39 -pkgrel=2 +pkgrel=3 pkgdesc='LTS Linux' url="https://www.kernel.org/" arch=(x86_64) @@ -18,6 +18,8 @@ config # the main kernel config file 0001-add-sysctl-and-CONFIG-for-unprivileged_userns_clone.patch 0001-gcc-common.h-Update-for-GCC-10.patch + 0002-Makefile-disallow-data-races-on-gcc-10-as-well.patch + 0003-x86-Fix-early-boot-crash-on-gcc-10-next-try.patch sphinx-workaround.patch ) validpgpkeys=( @@ -29,7 +31,9 @@ 'SKIP' '8b202067f6f0adbe2f8d4290624005f4fa1fff32aaa42f979c9ab03f6b74b62f' 'a13581d3c6dc595206e4fe7fcf6b542e7a1bdbe96101f0f010fc5be49f99baf2' - '5ccd721fea425fc9b1c08edf4f8ea94ee5737c193009b7a4253f7a383b273858' + '2b63997760aa823b5907c3c5653f35265e9c6320b812b4f4a8e7c74256dab7c7' + '875400c2dded3c05588025e0095b529c53f317abcccc99507eff0a75f24aa93f' + 'b7505c345722c4c1ca27c8d99114d4b8746e530acd9b7c4e5a0601b89bfba2d2' 'b7c814c8183e4645947a6dcc3cbf80431de8a8fd4e895b780f9a5fd92f82cb8e') export KBUILD_BUILD_HOST=archlinux