From 7053f80d96967d8e72e9f2a724bbfc3906ce2b07 Mon Sep 17 00:00:00 2001 From: Michael Ellerman Date: Fri, 20 Mar 2020 14:21:16 +1100 Subject: powerpc/64: Prevent stack protection in early boot The previous commit reduced the amount of code that is run before we setup a paca. However there are still a few remaining functions that run with no paca, or worse, with an arbitrary value in r13 that will be used as a paca pointer. In particular the stack protector canary is stored in the paca, so if stack protector is activated for any of these functions we will read the stack canary from wherever r13 points. If r13 happens to point outside of memory we will get a machine check / checkstop. For example if we modify initialise_paca() to trigger stack protection, and then boot in the mambo simulator with r13 poisoned in skiboot before calling the kernel: DEBUG: 19952232: (19952232): INSTRUCTION: PC=0xC0000000191FC1E8: [0x3C4C006D]: addis r2,r12,0x6D [fetch] DEBUG: 19952236: (19952236): INSTRUCTION: PC=0xC00000001807EAD8: [0x7D8802A6]: mflr r12 [fetch] FATAL ERROR: 19952276: (19952276): Check Stop for 0:0: Machine Check with ME bit of MSR off DEBUG: 19952276: (19952276): INSTRUCTION: PC=0xC0000000191FCA7C: [0xE90D0CF8]: ld r8,0xCF8(r13) [Instruction Failed] INFO: 19952276: (19952277): ** Execution stopped: Mambo Error, Machine Check Stop, ** systemsim % bt pc: 0xC0000000191FCA7C initialise_paca+0x54 lr: 0xC0000000191FC22C early_setup+0x44 stack:0x00000000198CBED0 0x0 +0x0 stack:0x00000000198CBF00 0xC0000000191FC22C early_setup+0x44 stack:0x00000000198CBF90 0x1801C968 +0x1801C968 So annotate the relevant functions to ensure stack protection is never enabled for them. Fixes: 06ec27aea9fc ("powerpc/64: add stack protector support") Cc: stable@vger.kernel.org # v4.20+ Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20200320032116.1024773-2-mpe@ellerman.id.au --- arch/powerpc/kernel/setup.h | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'arch/powerpc/kernel/setup.h') diff --git a/arch/powerpc/kernel/setup.h b/arch/powerpc/kernel/setup.h index 2dd0d9cb5a20..2ec835574cc9 100644 --- a/arch/powerpc/kernel/setup.h +++ b/arch/powerpc/kernel/setup.h @@ -8,6 +8,12 @@ #ifndef __ARCH_POWERPC_KERNEL_SETUP_H #define __ARCH_POWERPC_KERNEL_SETUP_H +#ifdef CONFIG_CC_IS_CLANG +#define __nostackprotector +#else +#define __nostackprotector __attribute__((__optimize__("no-stack-protector"))) +#endif + void initialize_cache_info(void); void irqstack_early_init(void); -- cgit v1.2.3