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SubjectRe: [PATCH] powerpc/code-patching: Relax verification of patchability
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Le 26/11/2021 à 08:39, Christophe Leroy a écrit :
> Commit 8b8a8f0ab3f5 ("powerpc/code-patching: Improve verification of
> patchability") introduced a stricter verification of the patched
> area by checking it is proper kernel text.
>
> But as least two usages of patch_instruction() fall outside:
> - Code patching selftests, which use stack and vmalloc space.
> - Ftrace
>
> So for the time being, partially revert commit 8b8a8f0ab3f5 and add
> a onetime warning:
>
> Running code patching self-tests ...
> patch_instruction() called on invalid text address 0xe1011e58 from test_code_patching+0x34/0xd6c
>
> Reported-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
> Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
> Cc: Nicholas Piggin <npiggin@gmail.com>
> Fixes: 8b8a8f0ab3f5 ("powerpc/code-patching: Improve verification of patchability")
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
> arch/powerpc/lib/code-patching.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
> index 1dd636a85cc1..c87eea773930 100644
> --- a/arch/powerpc/lib/code-patching.c
> +++ b/arch/powerpc/lib/code-patching.c
> @@ -190,9 +190,13 @@ static int do_patch_instruction(u32 *addr, struct ppc_inst instr)
> int patch_instruction(u32 *addr, struct ppc_inst instr)
> {
> /* Make sure we aren't patching a freed init section */
> - if (!kernel_text_address((unsigned long)addr))
> + if (system_state >= SYSTEM_FREEING_INITMEM && init_section_contains(addr, 4))
> return 0;
>
> + if (!kernel_text_address((unsigned long)addr))
> + pr_warn_once("%s() called on invalid text address 0x%p from %pS\n",
> + __func__, addr, __builtin_return_address(0));
> +

May it be better to use pr_warn_ratelimited() instead in order to catch
more than the first occurence ?

> return do_patch_instruction(addr, instr);
> }
> NOKPROBE_SYMBOL(patch_instruction);
>

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