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Date:   Wed, 30 Mar 2022 16:12:18 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     keescook@...omium.org
CC:     Paul Walmsley <paul.walmsley@...ive.com>, keescook@...omium.org,
        aou@...s.berkeley.edu, peterz@...radead.org, jszhang@...nel.org,
        geert@...ux-m68k.org, mark.rutland@....com, chenhuang5@...wei.com,
        linux-riscv@...ts.infradead.org, wangkefeng.wang@...wei.com,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject:     Re: [PATCH] riscv: Rename "sp_in_global" to "current_stack_pointer"

On Tue, 22 Mar 2022 19:16:28 PDT (-0700), Palmer Dabbelt wrote:
> On Wed, 23 Feb 2022 22:04:11 PST (-0800), keescook@...omium.org wrote:
>> To follow the existing per-arch conventions, rename "sp_in_global" to
>> "current_stack_pointer". This will let it be used in non-arch places
>> (like HARDENED_USERCOPY).
>>
>> Cc: Paul Walmsley <paul.walmsley@...ive.com>
>> Cc: Palmer Dabbelt <palmer@...belt.com>
>> Cc: Albert Ou <aou@...s.berkeley.edu>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: Jisheng Zhang <jszhang@...nel.org>
>> Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
>> Cc: Mark Rutland <mark.rutland@....com>
>> Cc: Chen Huang <chenhuang5@...wei.com>
>> Cc: linux-riscv@...ts.infradead.org
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> ---
>>  arch/riscv/Kconfig               | 1 +
>>  arch/riscv/include/asm/current.h | 2 ++
>>  arch/riscv/kernel/stacktrace.c   | 4 +---
>>  3 files changed, 4 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>> index 5adcbd9b5e88..b120c32697af 100644
>> --- a/arch/riscv/Kconfig
>> +++ b/arch/riscv/Kconfig
>> @@ -16,6 +16,7 @@ config RISCV
>>  	select ARCH_ENABLE_HUGEPAGE_MIGRATION if HUGETLB_PAGE && MIGRATION
>>  	select ARCH_ENABLE_SPLIT_PMD_PTLOCK if PGTABLE_LEVELS > 2
>>  	select ARCH_HAS_BINFMT_FLAT
>> +	select ARCH_HAS_CURRENT_STACK_POINTER
>>  	select ARCH_HAS_DEBUG_VM_PGTABLE
>>  	select ARCH_HAS_DEBUG_VIRTUAL if MMU
>>  	select ARCH_HAS_DEBUG_WX
>> diff --git a/arch/riscv/include/asm/current.h b/arch/riscv/include/asm/current.h
>> index 1de233d8e8de..21774d868c65 100644
>> --- a/arch/riscv/include/asm/current.h
>> +++ b/arch/riscv/include/asm/current.h
>> @@ -33,6 +33,8 @@ static __always_inline struct task_struct *get_current(void)
>>
>>  #define current get_current()
>>
>> +register unsigned long current_stack_pointer __asm__("sp");
>> +
>>  #endif /* __ASSEMBLY__ */
>>
>>  #endif /* _ASM_RISCV_CURRENT_H */
>> diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
>> index 201ee206fb57..278380e2e956 100644
>> --- a/arch/riscv/kernel/stacktrace.c
>> +++ b/arch/riscv/kernel/stacktrace.c
>> @@ -14,8 +14,6 @@
>>
>>  #include <asm/stacktrace.h>
>>
>> -register unsigned long sp_in_global __asm__("sp");
>> -
>>  #ifdef CONFIG_FRAME_POINTER
>>
>>  void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
>> @@ -77,7 +75,7 @@ void notrace walk_stackframe(struct task_struct *task,
>>  		sp = user_stack_pointer(regs);
>>  		pc = instruction_pointer(regs);
>>  	} else if (task == NULL || task == current) {
>> -		sp = sp_in_global;
>> +		sp = current_stack_pointer;
>>  		pc = (unsigned long)walk_stackframe;
>>  	} else {
>>  		/* task blocked in __switch_to */
>
> Sorry to be slow on this one.  This looks good, but another use of
> sp_in_global snuck into fixes and I don't merge fixes into for-next so
> that makes this a bit of a headache.
>
> There's a bunch of stuff in flight, so I'm going to hold off on this
> until after my first week's merge window PR.  I intend on merging the
> following, which is at palmer/riscv-sp for now (I'll probably just
> cherry-pick that, I usually start basing stuff on Linus' merge of my PR
> and just cherry-pick in single patches).
>
>    commit 7c4f6bb6fb352cfa6028191c2888356b9157a332
>    gpg: Signature made Tue 22 Mar 2022 11:12:19 AM PDT
>    gpg:                using RSA key 2B3C3747446843B24A943A7A2E1319F35FBB1889
>    gpg:                issuer "palmer@...belt.com"
>    gpg: Good signature from "Palmer Dabbelt <palmer@...belt.com>" [ultimate]
>    gpg:                 aka "Palmer Dabbelt <palmer@...osinc.com>" [ultimate]
>    Author: Kees Cook <keescook@...omium.org>
>    Date:   Wed Feb 23 22:04:11 2022 -0800
>
>        riscv: Rename "sp_in_global" to "current_stack_pointer"
>
>        To follow the existing per-arch conventions, rename "sp_in_global" to
>        "current_stack_pointer". This will let it be used in non-arch places
>        (like HARDENED_USERCOPY).
>
>        Signed-off-by: Kees Cook <keescook@...omium.org>
>        Signed-off-by: Palmer Dabbelt <palmer@...osinc.com>
>
>    diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>    index 5adcbd9b5e88..b120c32697af 100644
>    --- a/arch/riscv/Kconfig
>    +++ b/arch/riscv/Kconfig
>    @@ -16,6 +16,7 @@ config RISCV
>     	select ARCH_ENABLE_HUGEPAGE_MIGRATION if HUGETLB_PAGE && MIGRATION
>     	select ARCH_ENABLE_SPLIT_PMD_PTLOCK if PGTABLE_LEVELS > 2
>     	select ARCH_HAS_BINFMT_FLAT
>    +	select ARCH_HAS_CURRENT_STACK_POINTER
>     	select ARCH_HAS_DEBUG_VM_PGTABLE
>     	select ARCH_HAS_DEBUG_VIRTUAL if MMU
>     	select ARCH_HAS_DEBUG_WX
>    diff --git a/arch/riscv/include/asm/current.h b/arch/riscv/include/asm/current.h
>    index 1de233d8e8de..21774d868c65 100644
>    --- a/arch/riscv/include/asm/current.h
>    +++ b/arch/riscv/include/asm/current.h
>    @@ -33,6 +33,8 @@ static __always_inline struct task_struct *get_current(void)
>
>     #define current get_current()
>
>    +register unsigned long current_stack_pointer __asm__("sp");
>    +
>     #endif /* __ASSEMBLY__ */
>
>     #endif /* _ASM_RISCV_CURRENT_H */
>    diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
>    index 14d2b53ec322..08d11a53f39e 100644
>    --- a/arch/riscv/kernel/stacktrace.c
>    +++ b/arch/riscv/kernel/stacktrace.c
>    @@ -14,8 +14,6 @@
>
>     #include <asm/stacktrace.h>
>
>    -register unsigned long sp_in_global __asm__("sp");
>    -
>     #ifdef CONFIG_FRAME_POINTER
>
>     void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
>    @@ -30,7 +28,7 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
>     		pc = instruction_pointer(regs);
>     	} else if (task == NULL || task == current) {
>     		fp = (unsigned long)__builtin_frame_address(0);
>    -		sp = sp_in_global;
>    +		sp = current_stack_pointer;
>     		pc = (unsigned long)walk_stackframe;
>     	} else {
>     		/* task blocked in __switch_to */
>    @@ -78,7 +76,7 @@ void notrace walk_stackframe(struct task_struct *task,
>     		sp = user_stack_pointer(regs);
>     		pc = instruction_pointer(regs);
>     	} else if (task == NULL || task == current) {
>    -		sp = sp_in_global;
>    +		sp = current_stack_pointer;
>     		pc = (unsigned long)walk_stackframe;
>     	} else {
>     		/* task blocked in __switch_to */
>
> Thanks!

Thanks, this is on for-next.  I put HARDENED_USERCOPY=y test in for SLAB 
and SLUB, not sure if there's anything else that's interesting to test 
(we're missing some bits needed for STACKLEAK).

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