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Date:   Wed, 30 Mar 2022 21:59:37 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Palmer Dabbelt <palmer@...belt.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>, 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 Wed, Mar 30, 2022 at 04:12:18PM -0700, Palmer Dabbelt wrote:
> 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).

Excellent; thank you!

-- 
Kees Cook

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