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Date:   Tue, 3 Oct 2023 09:35:33 -0700
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Subject: Re: [PATCH v2] arch: Reserve map_shadow_stack() syscall number for
 all architectures
To:     <linux-api@vger.kernel.org>, <linux-arch@vger.kernel.org>,
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References: <20230914185804.2000497-1-sohil.mehta@intel.com>
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From:   Sohil Mehta <sohil.mehta@intel.com>
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On 9/14/2023 11:58 AM, Sohil Mehta wrote:
> commit c35559f94ebc ("x86/shstk: Introduce map_shadow_stack syscall")
> recently added support for map_shadow_stack() but it is limited to x86
> only for now. There is a possibility that other architectures (namely,
> arm64 and RISC-V), that are implementing equivalent support for shadow
> stacks, might need to add support for it.
> 
> Independent of that, reserving arch-specific syscall numbers in the
> syscall tables of all architectures is good practice and would help
> avoid future conflicts. map_shadow_stack() is marked as a conditional
> syscall in sys_ni.c. Adding it to the syscall tables of other
> architectures is harmless and would return ENOSYS when exercised.
> 
> Note, map_shadow_stack() was assigned #453 during the merge process
> since #452 was taken by fchmodat2().
> 
> For Powerpc, map it to sys_ni_syscall() as is the norm for Powerpc
> syscall tables.
> 
> For Alpha, map_shadow_stack() takes up #563 as Alpha still diverges from
> the common syscall numbering system in the other architectures.
> 
> Link: https://lore.kernel.org/lkml/20230515212255.GA562920@debug.ba.rivosinc.com/
> Link: https://lore.kernel.org/lkml/b402b80b-a7c6-4ef0-b977-c0f5f582b78a@sirena.org.uk/
> 
> Signed-off-by: Sohil Mehta <sohil.mehta@intel.com>
> ---

Gentle ping...

Are there any additional comments? It applies cleanly on 6.6-rc4.

Or does it seem ready to be merged? It has the following
acknowledgements until now:

Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)

>  arch/alpha/kernel/syscalls/syscall.tbl      | 1 +
>  arch/arm/tools/syscall.tbl                  | 1 +
>  arch/arm64/include/asm/unistd.h             | 2 +-
>  arch/arm64/include/asm/unistd32.h           | 2 ++
>  arch/ia64/kernel/syscalls/syscall.tbl       | 1 +
>  arch/m68k/kernel/syscalls/syscall.tbl       | 1 +
>  arch/microblaze/kernel/syscalls/syscall.tbl | 1 +
>  arch/mips/kernel/syscalls/syscall_n32.tbl   | 1 +
>  arch/mips/kernel/syscalls/syscall_n64.tbl   | 1 +
>  arch/mips/kernel/syscalls/syscall_o32.tbl   | 1 +
>  arch/parisc/kernel/syscalls/syscall.tbl     | 1 +
>  arch/powerpc/kernel/syscalls/syscall.tbl    | 1 +
>  arch/s390/kernel/syscalls/syscall.tbl       | 1 +
>  arch/sh/kernel/syscalls/syscall.tbl         | 1 +
>  arch/sparc/kernel/syscalls/syscall.tbl      | 1 +
>  arch/x86/entry/syscalls/syscall_32.tbl      | 1 +
>  arch/xtensa/kernel/syscalls/syscall.tbl     | 1 +
>  include/uapi/asm-generic/unistd.h           | 5 ++++-
>  18 files changed, 22 insertions(+), 2 deletions(-)
>> diff --git a/arch/alpha/kernel/syscalls/syscall.tbl
b/arch/alpha/kernel/syscalls/syscall.tbl
> index ad37569d0507..6e8479c96e65 100644
> --- a/arch/alpha/kernel/syscalls/syscall.tbl
> +++ b/arch/alpha/kernel/syscalls/syscall.tbl
> @@ -492,3 +492,4 @@
>  560	common	set_mempolicy_home_node		sys_ni_syscall
>  561	common	cachestat			sys_cachestat
>  562	common	fchmodat2			sys_fchmodat2
> +563	common	map_shadow_stack		sys_map_shadow_stack
> diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
> index c572d6c3dee0..6d494dfbf5e4 100644
> --- a/arch/arm/tools/syscall.tbl
> +++ b/arch/arm/tools/syscall.tbl
> @@ -466,3 +466,4 @@
>  450	common	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
> diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h
> index bd77253b62e0..6a28fb91b85d 100644
> --- a/arch/arm64/include/asm/unistd.h
> +++ b/arch/arm64/include/asm/unistd.h
> @@ -39,7 +39,7 @@
>  #define __ARM_NR_compat_set_tls		(__ARM_NR_COMPAT_BASE + 5)
>  #define __ARM_NR_COMPAT_END		(__ARM_NR_COMPAT_BASE + 0x800)
>  
> -#define __NR_compat_syscalls		453
> +#define __NR_compat_syscalls		454
>  #endif
>  
>  #define __ARCH_WANT_SYS_CLONE
> diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h
> index 78b68311ec81..a201d842ec82 100644
> --- a/arch/arm64/include/asm/unistd32.h
> +++ b/arch/arm64/include/asm/unistd32.h
> @@ -911,6 +911,8 @@ __SYSCALL(__NR_set_mempolicy_home_node, sys_set_mempolicy_home_node)
>  __SYSCALL(__NR_cachestat, sys_cachestat)
>  #define __NR_fchmodat2 452
>  __SYSCALL(__NR_fchmodat2, sys_fchmodat2)
> +#define __NR_map_shadow_stack 453
> +__SYSCALL(__NR_map_shadow_stack, sys_map_shadow_stack)
>  
>  /*
>   * Please add new compat syscalls above this comment and update
> diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl
> index 83d8609aec03..be02ce9d376f 100644
> --- a/arch/ia64/kernel/syscalls/syscall.tbl
> +++ b/arch/ia64/kernel/syscalls/syscall.tbl
> @@ -373,3 +373,4 @@
>  450	common	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
> diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
> index 259ceb125367..bee2d2f7f82c 100644
> --- a/arch/m68k/kernel/syscalls/syscall.tbl
> +++ b/arch/m68k/kernel/syscalls/syscall.tbl
> @@ -452,3 +452,4 @@
>  450	common	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
> diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
> index a3798c2637fd..09eda7ed91b0 100644
> --- a/arch/microblaze/kernel/syscalls/syscall.tbl
> +++ b/arch/microblaze/kernel/syscalls/syscall.tbl
> @@ -458,3 +458,4 @@
>  450	common	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
> diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl
> index 152034b8e0a0..3c02cc3886ca 100644
> --- a/arch/mips/kernel/syscalls/syscall_n32.tbl
> +++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
> @@ -391,3 +391,4 @@
>  450	n32	set_mempolicy_home_node		sys_set_mempolicy_home_node
>  451	n32	cachestat			sys_cachestat
>  452	n32	fchmodat2			sys_fchmodat2
> +453	n32	map_shadow_stack		sys_map_shadow_stack
> diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl
> index cb5e757f6621..aa9ed6a7cb48 100644
> --- a/arch/mips/kernel/syscalls/syscall_n64.tbl
> +++ b/arch/mips/kernel/syscalls/syscall_n64.tbl
> @@ -367,3 +367,4 @@
>  450	common	set_mempolicy_home_node		sys_set_mempolicy_home_node
>  451	n64	cachestat			sys_cachestat
>  452	n64	fchmodat2			sys_fchmodat2
> +453	n64	map_shadow_stack		sys_map_shadow_stack
> diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl
> index 1a646813afdc..756f6feb21c2 100644
> --- a/arch/mips/kernel/syscalls/syscall_o32.tbl
> +++ b/arch/mips/kernel/syscalls/syscall_o32.tbl
> @@ -440,3 +440,4 @@
>  450	o32	set_mempolicy_home_node		sys_set_mempolicy_home_node
>  451	o32	cachestat			sys_cachestat
>  452	o32	fchmodat2			sys_fchmodat2
> +453	o32	map_shadow_stack		sys_map_shadow_stack
> diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
> index e97c175b56f9..c80eedbe0170 100644
> --- a/arch/parisc/kernel/syscalls/syscall.tbl
> +++ b/arch/parisc/kernel/syscalls/syscall.tbl
> @@ -451,3 +451,4 @@
>  450	common	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
> diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
> index 20e50586e8a2..87a54acf8346 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_home_node
>  451	common	cachestat			sys_cachestat
>  452	common	fchmodat2			sys_fchmodat2
> +453	common	map_shadow_stack		sys_ni_syscall
> diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
> index 0122cc156952..22249c07e556 100644
> --- a/arch/s390/kernel/syscalls/syscall.tbl
> +++ b/arch/s390/kernel/syscalls/syscall.tbl
> @@ -455,3 +455,4 @@
>  450  common	set_mempolicy_home_node	sys_set_mempolicy_home_node	sys_set_mempolicy_home_node
>  451  common	cachestat		sys_cachestat			sys_cachestat
>  452  common	fchmodat2		sys_fchmodat2			sys_fchmodat2
> +453  common	map_shadow_stack	sys_map_shadow_stack		sys_map_shadow_stack
> diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
> index e90d585c4d3e..5ccfe6fbb6b1 100644
> --- a/arch/sh/kernel/syscalls/syscall.tbl
> +++ b/arch/sh/kernel/syscalls/syscall.tbl
> @@ -455,3 +455,4 @@
>  450	common	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
> diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
> index 4ed06c71c43f..b2d664edebdd 100644
> --- a/arch/sparc/kernel/syscalls/syscall.tbl
> +++ b/arch/sparc/kernel/syscalls/syscall.tbl
> @@ -498,3 +498,4 @@
>  450	common	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
> diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
> index 2d0b1bd866ea..743a7ef5a4b9 100644
> --- a/arch/x86/entry/syscalls/syscall_32.tbl
> +++ b/arch/x86/entry/syscalls/syscall_32.tbl
> @@ -457,3 +457,4 @@
>  450	i386	set_mempolicy_home_node		sys_set_mempolicy_home_node
>  451	i386	cachestat		sys_cachestat
>  452	i386	fchmodat2		sys_fchmodat2
> +453	i386	map_shadow_stack	sys_map_shadow_stack
> diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl
> index fc1a4f3c81d9..94e6bcc2bec7 100644
> --- a/arch/xtensa/kernel/syscalls/syscall.tbl
> +++ b/arch/xtensa/kernel/syscalls/syscall.tbl
> @@ -423,3 +423,4 @@
>  450	common	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
> diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
> index abe087c53b4b..203ae30d7761 100644
> --- a/include/uapi/asm-generic/unistd.h
> +++ b/include/uapi/asm-generic/unistd.h
> @@ -823,8 +823,11 @@ __SYSCALL(__NR_cachestat, sys_cachestat)
>  #define __NR_fchmodat2 452
>  __SYSCALL(__NR_fchmodat2, sys_fchmodat2)
>  
> +#define __NR_map_shadow_stack 453
> +__SYSCALL(__NR_map_shadow_stack, sys_map_shadow_stack)
> +
>  #undef __NR_syscalls
> -#define __NR_syscalls 453
> +#define __NR_syscalls 454
>  
>  /*
>   * 32 bit systems traditionally used different
> --