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Message-ID: <20230428151837.GD1449475@hirez.programming.kicks-ass.net>
Date: Fri, 28 Apr 2023 17:18:37 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Hou Wenlong <houwenlong.hwl@...group.com>
Cc: linux-kernel@...r.kernel.org,
Thomas Garnier <thgarnie@...omium.org>,
Lai Jiangshan <jiangshan.ljs@...group.com>,
Kees Cook <keescook@...omium.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>,
Josh Poimboeuf <jpoimboe@...nel.org>,
Christophe Leroy <christophe.leroy@...roup.eu>,
Sathvika Vasireddy <sv@...ux.ibm.com>
Subject: Re: [PATCH RFC 34/43] objtool: Adapt indirect call of __fentry__()
for PIE support
On Fri, Apr 28, 2023 at 05:51:14PM +0800, Hou Wenlong wrote:
> --- a/tools/objtool/arch/x86/decode.c
> +++ b/tools/objtool/arch/x86/decode.c
> @@ -747,15 +747,21 @@ void arch_initial_func_cfi_state(struct cfi_init_state *state)
>
> const char *arch_nop_insn(int len)
> {
> - static const char nops[5][5] = {
> + static const char nops[6][6] = {
> { BYTES_NOP1 },
> { BYTES_NOP2 },
> { BYTES_NOP3 },
> { BYTES_NOP4 },
> { BYTES_NOP5 },
> + /*
> + * For PIE kernel, use a 5-byte nop
> + * and 1-byte nop to keep the frace
> + * hooking algorithm working correct.
> + */
> + { BYTES_NOP5, BYTES_NOP1 },
> };
> - if (len < 1 || len > 5) {
> + if (len < 1 || len > 6) {
> WARN("invalid NOP size: %d\n", len);
> return NULL;
> }
Like Steve already said, this is broken, we hard rely on these things
being single instructions, this must absolutely be BYTES_NOP6.
And yes, then you get to fix a whole lot more.
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