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powerpc: Avoid broken GCC __attribute__((optimize))

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[ Upstream commit a7223f5bfcaeade4a86d35263493bcda6c940891 ]

Commit 7053f80d9696 ("powerpc/64: Prevent stack protection in early
boot") introduced a couple of uses of __attribute__((optimize)) with
function scope, to disable the stack protector in some early boot
code.

Unfortunately, and this is documented in the GCC man pages [0],
overriding function attributes for optimization is broken, and is only
supported for debug scenarios, not for production: the problem appears
to be that setting GCC -f flags using this method will cause it to
forget about some or all other optimization settings that have been
applied.

So the only safe way to disable the stack protector is to disable it
for the entire source file.

[0] https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html

Fixes: 7053f80d9696 ("powerpc/64: Prevent stack protection in early boot")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
[mpe: Drop one remaining use of __nostackprotector, reported by snowpatch]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201028080433.26799-1-ardb@kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Ard Biesheuvel 2020-10-28 09:04:33 +01:00 committed by Greg Kroah-Hartman
parent 8f6e6ec101
commit 90b39366d8
4 changed files with 6 additions and 9 deletions
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3
arch/powerpc/kernel/Makefile
View File

@ -181,6 +181,9 @@ KCOV_INSTRUMENT_cputable.o := n
KCOV_INSTRUMENT_setup_64.o := n
KCOV_INSTRUMENT_paca.o := n
CFLAGS_setup_64.o += -fno-stack-protector
CFLAGS_paca.o += -fno-stack-protector
extra-$(CONFIG_PPC_FPU) += fpu.o
extra-$(CONFIG_ALTIVEC) += vector.o
extra-$(CONFIG_PPC64) += entry_64.o

4
arch/powerpc/kernel/paca.c
View File

@ -176,7 +176,7 @@ static struct slb_shadow * __init new_slb_shadow(int cpu, unsigned long limit)
struct paca_struct **paca_ptrs __read_mostly;
EXPORT_SYMBOL(paca_ptrs);
void __init __nostackprotector initialise_paca(struct paca_struct *new_paca, int cpu)
void __init initialise_paca(struct paca_struct *new_paca, int cpu)
{
#ifdef CONFIG_PPC_PSERIES
new_paca->lppaca_ptr = NULL;
@ -205,7 +205,7 @@ void __init __nostackprotector initialise_paca(struct paca_struct *new_paca, int
}
/* Put the paca pointer into r13 and SPRG_PACA */
void __nostackprotector setup_paca(struct paca_struct *new_paca)
void setup_paca(struct paca_struct *new_paca)
{
/* Setup r13 */
local_paca = new_paca;

6
arch/powerpc/kernel/setup.h
View File

@ -8,12 +8,6 @@
#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);

2
arch/powerpc/kernel/setup_64.c
View File

@ -284,7 +284,7 @@ void __init record_spr_defaults(void)
* device-tree is not accessible via normal means at this point.
*/
void __init __nostackprotector early_setup(unsigned long dt_ptr)
void __init early_setup(unsigned long dt_ptr)
{
static __initdata struct paca_struct boot_paca;