powerpc/32: add stack protector support
authorChristophe Leroy <christophe.leroy@c-s.fr>
Thu, 27 Sep 2018 07:05:53 +0000 (07:05 +0000)
committerMichael Ellerman <mpe@ellerman.id.au>
Wed, 3 Oct 2018 05:40:03 +0000 (15:40 +1000)
commitc3ff2a5193fa61b1b284cfb1d79628814ed0e95a
tree042c4265fbe1dac941bd5c6c9d2079c1d8bdde14
parentcd5ff94577e004e0a4457e70d0ef3a030f4010b8
powerpc/32: add stack protector support

This functionality was tentatively added in the past
(commit 6533b7c16ee5 ("powerpc: Initial stack protector
(-fstack-protector) support")) but had to be reverted
(commit f2574030b0e3 ("powerpc: Revert the initial stack
protector support") because of GCC implementing it differently
whether it had been built with libc support or not.

Now, GCC offers the possibility to manually set the
stack-protector mode (global or tls) regardless of libc support.

This time, the patch selects HAVE_STACKPROTECTOR only if
-mstack-protector-guard=tls is supported by GCC.

On PPC32, as register r2 points to current task_struct at
all time, the stack_canary located inside task_struct can be
used directly by using the following GCC options:
-mstack-protector-guard=tls
-mstack-protector-guard-reg=r2
-mstack-protector-guard-offset=offsetof(struct task_struct, stack_canary))

The protector is disabled for prom_init and bootx_init as
it is too early to handle it properly.

 $ echo CORRUPT_STACK > /sys/kernel/debug/provoke-crash/DIRECT
[  134.943666] Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: lkdtm_CORRUPT_STACK+0x64/0x64
[  134.943666]
[  134.955414] CPU: 0 PID: 283 Comm: sh Not tainted 4.18.0-s3k-dev-12143-ga3272be41209 #835
[  134.963380] Call Trace:
[  134.965860] [c6615d60] [c001f76c] panic+0x118/0x260 (unreliable)
[  134.971775] [c6615dc0] [c001f654] panic+0x0/0x260
[  134.976435] [c6615dd0] [c032c368] lkdtm_CORRUPT_STACK_STRONG+0x0/0x64
[  134.982769] [c6615e00] [ffffffff] 0xffffffff

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
arch/powerpc/Kconfig
arch/powerpc/Makefile
arch/powerpc/include/asm/stackprotector.h [new file with mode: 0644]
arch/powerpc/kernel/Makefile
arch/powerpc/kernel/asm-offsets.c
arch/powerpc/platforms/powermac/Makefile