[v5,1/2] powerpc/32: add stack protector support

[Michael Ellerman]

On Thu, 2018-09-27 at 07:05:53 UTC, Christophe Leroy wrote:
> 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 at c-s.fr>

Series applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/c3ff2a5193fa61b1b284cfb1d79628

cheers