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powerpc/code-patching: Use dedicated memory routines for patching

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The patching page set up as a writable alias may be in quadrant 0
(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 EAA is privileged access only, RW). It just happens to be in
quadrant 0 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 <bgray@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240325052815.854044-2-bgray@linux.ibm.com
This commit is contained in:
Benjamin Gray 2024-03-25 16:28:15 +11:00 • committed by Michael Ellerman
parent c5ef5e3584
commit c3710ee7cd
1 changed files with 27 additions and 4 deletions
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31
arch/powerpc/lib/code-patching.c
View file

@ -372,9 +372,32 @@ 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;
}
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_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 +406,19 @@ 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 = copy_to_kernel_nofault(patch_addr, code, len);
}
smp_wmb(); /* smp write barrier */
flush_icache_range(start, start + len);
return 0;
return err;
}
/*