On Fri, 2024-03-15 at 06:36 +0000, Christophe Leroy wrote:
>
>
> Le 15/03/2024 à 03:57, Benjamin Gray a écrit :
> > The patching page set up as a writable alias may be in quadrant 1
> > (userspace) if the temporary mm path is used. This causes sanitiser
> > failures if so. Sanitiser failures also occur on the non-mm path
> > because the plain memset family is instrumented, and KASAN treats
> > the
> > patching window as poisoned.
> >
> > Introduce locally defined patch_* variants of memset that perform
> > an
> > uninstrumented lower level set, as well as detecting write errors
> > like
> > the original single patch variant does.
> >
> > copy_to_user() is not correct here, as the PTE makes it a proper
> > kernel
> > page (the EEA is privileged access only, RW). It just happens to be
> > in
> > quadrant 1 because that's the hardware's mechanism for using the
> > current
> > PID vs PID 0 in translations. Importantly, it's incorrect to allow
> > user
> > page accesses.
> >
> > Now that the patching memsets are used, we also propagate a failure
> > up
> > to the caller as the single patch variant does.
> >
> > Signed-off-by: Benjamin Gray <bg...@linux.ibm.com>
> >
> > ---
> >
> > The patch_memcpy() can be optimised to 4 bytes at a time assuming
> > the
> > same requirements as regular instruction patching are being
> > followed
> > for the 'copy sequence of instructions' mode (i.e., they actually
> > are
> > instructions following instruction alignment rules).
>
> Why not use copy_to_kernel_nofault() ?
I had not come across copy_to_kernel_nofault(). It looks like the
optimised memcpy() I wanted, so thanks.
>
>
> > ---
> > arch/powerpc/lib/code-patching.c | 42
> > +++++++++++++++++++++++++++++---
> > 1 file changed, 38 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/powerpc/lib/code-patching.c
> > b/arch/powerpc/lib/code-patching.c
> > index c6ab46156cda..c6633759b509 100644
> > --- a/arch/powerpc/lib/code-patching.c
> > +++ b/arch/powerpc/lib/code-patching.c
> > @@ -372,9 +372,43 @@ int patch_instruction(u32 *addr, ppc_inst_t
> > instr)
> > }
> > NOKPROBE_SYMBOL(patch_instruction);
> >
> > +static int patch_memset64(u64 *addr, u64 val, size_t count)
> > +{
> > + for (u64 *end = addr + count; addr < end; addr++)
> > + __put_kernel_nofault(addr, &val, u64, failed);
> > +
> > + return 0;
> > +
> > +failed:
> > + return -EPERM;
>
> Is it correct ? Shouldn't it be -EFAULT ?
The single instruction patch returns EPERM, which was set this way to
align with ftrace's expectations. I think it's best to keep the
single/multi patching variants consistent with each other where
possible.
>
> > +}
> > +
> > +static int patch_memset32(u32 *addr, u32 val, size_t count)
> > +{
> > + for (u32 *end = addr + count; addr < end; addr++)
> > + __put_kernel_nofault(addr, &val, u32, failed);
> > +
> > + return 0;
> > +
> > +failed:
> > + return -EPERM;
> > +}
> > +
> > +static int patch_memcpy(void *dst, void *src, size_t len)
> > +{
> > + for (void *end = src + len; src < end; dst++, src++)
> > + __put_kernel_nofault(dst, src, u8, failed);
> > +
> > + return 0;
> > +
> > +failed:
> > + return -EPERM;
> > +}
> > +
> > static int __patch_instructions(u32 *patch_addr, u32 *code,
> > size_t len, bool repeat_instr)
> > {
> > unsigned long start = (unsigned long)patch_addr;
> > + int err;
> >
> > /* Repeat instruction */
> > if (repeat_instr) {
> > @@ -383,19 +417,19 @@ static int __patch_instructions(u32
> > *patch_addr, u32 *code, size_t len, bool rep
> > if (ppc_inst_prefixed(instr)) {
> > u64 val = ppc_inst_as_ulong(instr);
> >
> > - memset64((u64 *)patch_addr, val, len / 8);
> > + err = patch_memset64((u64 *)patch_addr,
> > val, len / 8);
> > } else {
> > u32 val = ppc_inst_val(instr);
> >
> > - memset32(patch_addr, val, len / 4);
> > + err = patch_memset32(patch_addr, val, len
> > / 4);
> > }
> > } else {
> > - memcpy(patch_addr, code, len);
> > + err = patch_memcpy(patch_addr, code, len);
>
> Use copy_to_kernel_nofault() instead of open coding a new less
> optimised
> version of it.
>
> > }
> >
> > smp_wmb(); /* smp write barrier */
> > flush_icache_range(start, start + len);
> > - return 0;
> > + return err;
> > }
> >
> > /*
