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() ?
> ---
> 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 ?
> +}
> +
> +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;
> }
>
> /*
