Re: [PATCH v7 11/11] arm64: scs: add shadow stacks for SDEI

Hi Sami,

On 12/02/2020 20:59, Sami Tolvanen wrote:

On Tue, Feb 11, 2020 at 5:57 AM James Morse [off-list ref] wrote:

quoted

On 28/01/2020 18:49, Sami Tolvanen wrote:

quoted

This change adds per-CPU shadow call stacks for the SDEI handler.
Similarly to how the kernel stacks are handled, we add separate shadow
stacks for normal and critical events.

Reviewed-by: James Morse <james.morse@arm.com>
Tested-by: James Morse <james.morse@arm.com>

quoted

quoted

diff --git a/arch/arm64/kernel/scs.c b/arch/arm64/kernel/scs.c
index eaadf5430baa..dddb7c56518b 100644
--- a/arch/arm64/kernel/scs.c
+++ b/arch/arm64/kernel/scs.c

quoted

+static int scs_alloc_percpu(unsigned long * __percpu *ptr, int cpu)
+{
+     unsigned long *p;
+
+     p = __vmalloc_node_range(PAGE_SIZE, SCS_SIZE,
+                              VMALLOC_START, VMALLOC_END,
+                              GFP_SCS, PAGE_KERNEL,
+                              0, cpu_to_node(cpu),
+                              __builtin_return_address(0));

(What makes this arch specific? arm64 has its own calls like this for the regular vmap
stacks because it plays tricks with the alignment. Here the alignment requirement comes
from the core SCS code... Would another architecture implement these
scs_alloc_percpu()/scs_free_percpu() differently?)

You are correct, these aren't necessarily specific to arm64. However,
right now, we are not allocating per-CPU shadow stacks anywhere else,
so this was a natural place for the helper functions.

Fair enough,

Would you prefer me to move these to kernel/scs.c instead?

I have no preference, as long as they don't get duplicated later!


Thanks,

James

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