| Message ID | 20210914152742.27047-1-amit.kachhap@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64/traps: Avoid unnecessary kernel/user pointer conversion | expand |
On Tue, Sep 14, 2021 at 08:57:42PM +0530, Amit Daniel Kachhap wrote: > Annotating a pointer from kernel to __user and then back again might > confuse sparse. In call_undef_hook() it can be avoided by not using the > intermediate user pointer variable. When you say "might confuse sparse", does it complain today? If so, can you include an example of what goes wrong? > Note: This patch adds no functional changes to code. > > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Will Deacon <will@kernel.org> > Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com> > --- > arch/arm64/kernel/traps.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c > index b03e383d944a..357d10a8bbf5 100644 > --- a/arch/arm64/kernel/traps.c > +++ b/arch/arm64/kernel/traps.c > @@ -404,7 +404,8 @@ static int call_undef_hook(struct pt_regs *regs) > > if (!user_mode(regs)) { > __le32 instr_le; > - if (get_kernel_nofault(instr_le, (__force __le32 *)pc)) > + if (get_kernel_nofault(instr_le, > + (__le32 *)instruction_pointer(regs))) Can we make `pc` an unsigned long, instead? It'd be nice to handle all three cases consistently, even if that means adding __force to the two user cases. Thanks, Mark. > goto exit; > instr = le32_to_cpu(instr_le); > } else if (compat_thumb_mode(regs)) { > -- > 2.17.1 >
Hi, On 9/14/21 9:30 PM, Mark Rutland wrote: > On Tue, Sep 14, 2021 at 08:57:42PM +0530, Amit Daniel Kachhap wrote: >> Annotating a pointer from kernel to __user and then back again might >> confuse sparse. In call_undef_hook() it can be avoided by not using the >> intermediate user pointer variable. > > When you say "might confuse sparse", does it complain today? If so, can > you include an example of what goes wrong? No it does not give warning. The __force option silences the warning. My idea is to remove the unwanted __force annotations and not mix user and kernel pointers. > >> Note: This patch adds no functional changes to code. >> >> Cc: Catalin Marinas <catalin.marinas@arm.com> >> Cc: Will Deacon <will@kernel.org> >> Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com> >> --- >> arch/arm64/kernel/traps.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c >> index b03e383d944a..357d10a8bbf5 100644 >> --- a/arch/arm64/kernel/traps.c >> +++ b/arch/arm64/kernel/traps.c >> @@ -404,7 +404,8 @@ static int call_undef_hook(struct pt_regs *regs) >> >> if (!user_mode(regs)) { >> __le32 instr_le; >> - if (get_kernel_nofault(instr_le, (__force __le32 *)pc)) >> + if (get_kernel_nofault(instr_le, >> + (__le32 *)instruction_pointer(regs))) > > Can we make `pc` an unsigned long, instead? I think it can be done. > > It'd be nice to handle all three cases consistently, even if that means > adding __force to the two user cases. Agree with your suggestion. Even in the 2 user cases, __force may not be needed as the typecast will be from from unsigned long to user pointer. BR, Amit > > Thanks, > Mark. > >> goto exit; >> instr = le32_to_cpu(instr_le); >> } else if (compat_thumb_mode(regs)) { >> -- >> 2.17.1 >>
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c index b03e383d944a..357d10a8bbf5 100644 --- a/arch/arm64/kernel/traps.c +++ b/arch/arm64/kernel/traps.c @@ -404,7 +404,8 @@ static int call_undef_hook(struct pt_regs *regs) if (!user_mode(regs)) { __le32 instr_le; - if (get_kernel_nofault(instr_le, (__force __le32 *)pc)) + if (get_kernel_nofault(instr_le, + (__le32 *)instruction_pointer(regs))) goto exit; instr = le32_to_cpu(instr_le); } else if (compat_thumb_mode(regs)) {
Annotating a pointer from kernel to __user and then back again might confuse sparse. In call_undef_hook() it can be avoided by not using the intermediate user pointer variable. Note: This patch adds no functional changes to code. Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com> --- arch/arm64/kernel/traps.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)