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powerpc: Avoid broken GCC __attribute__((optimize))

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[ Upstream commit a7223f5bfcaeade4a86d35263493bcda6c940891 ]

Commit 7053f80d96 ("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: 7053f80d96 ("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 6014c6ed74
commit b1a0097b82
4 changed files with 6 additions and 9 deletions
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2
arch/powerpc/kernel/setup_64.c
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@@ -283,7 +283,7 @@ 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;