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Message-ID: <29da2af0-5c88-f937-a9b6-db2d5f481321@intel.com>
Date: Wed, 13 Sep 2023 12:18:28 -0700
From: Sohil Mehta <sohil.mehta@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
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Subject: Re: [PATCH 2/2] arch: Reserve map_shadow_stack() syscall number for
all architectures
On 9/11/2023 2:10 PM, Edgecombe, Rick P wrote:
> On Mon, 2023-09-11 at 18:02 +0000, Sohil Mehta wrote:
>> diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl
>> b/arch/powerpc/kernel/syscalls/syscall.tbl
>> index 20e50586e8a2..2767b8a42636 100644
>> --- a/arch/powerpc/kernel/syscalls/syscall.tbl
>> +++ b/arch/powerpc/kernel/syscalls/syscall.tbl
>> @@ -539,3 +539,4 @@
>> 450 nospu set_mempolicy_home_node sys_set_mempolicy_hom
>> e_node
>> 451 common cachestat sys_cachestat
>> 452 common fchmodat2 sys_fchmodat2
>> +453 common map_shadow_stack sys_map_shadow_stack
>
> I noticed in powerpc, the not implemented syscalls are manually mapped
> to sys_ni_syscall. It also has some special extra sys_ni_syscall()
> implementation bits to handle both ARCH_HAS_SYSCALL_WRAPPER and
> !ARCH_HAS_SYSCALL_WRAPPER. So wondering if it might need special
> treatment. Did you see those parts?
>
Thanks for pointing this out. Powerpc seems to be unique in their
handling of not implemented syscalls. Maybe it's because of their
special casing of the ARCH_HAS_SYSCALL_WRAPPER.
The code below in arch/powerpc/include/asm/syscalls.h suggests to me
that it should be safe to map map_shadow_stack() to sys_ni_syscall() and
the special handling will be taken care of.
#ifndef CONFIG_ARCH_HAS_SYSCALL_WRAPPER
long sys_ni_syscall(void);
#else
long sys_ni_syscall(const struct pt_regs *regs);
#endif
I don't quite understand the underlying reasoning for it though. Do you
have any additional insight into how we should handle this?
I am thinking of doing the following in the next iteration unless
someone chimes in and says otherwise.
--- a/arch/powerpc/kernel/syscalls/syscall.tbl
+++ b/arch/powerpc/kernel/syscalls/syscall.tbl
@@ -539,4 +539,4 @@
450 nospu set_mempolicy_home_node sys_set_mempolicy_home_node
451 common cachestat sys_cachestat
452 common fchmodat2 sys_fchmodat2
-453 common map_shadow_stack sys_map_shadow_stack
+453 common map_shadow_stack sys_ni_syscall
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