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Message-ID: <Y906d8b6xhC17AAV@zn.tnic>
Date: Fri, 3 Feb 2023 17:46:47 +0100
From: Borislav Petkov <bp@...en8.de>
To: Peter Zijlstra <peterz@...radead.org>
Cc: x86@...nel.org, Masami Hiramatsu <mhiramat@...nel.org>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Andrew Cooper <Andrew.Cooper3@...rix.com>,
Josh Poimboeuf <jpoimboe@...hat.com>,
linux-kernel@...r.kernel.org
Subject: Re: [RFC] x86/alternative: Support relocations in alternatives
On Fri, Feb 03, 2023 at 05:04:35PM +0100, Borislav Petkov wrote:
> Rest on IRC. :)
Here's what I'm thinking. It still fails somewhere while booting so it
is not good yet but the idea is to show what I mean:
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 0eff4033eea4..2ede814de089 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -208,14 +208,23 @@ apply_reloc(int n, void *ptr, uintptr_t diff)
}
}
+static void __always_inline apply_new_offset(int immed_size, void *ptr, s32 new_offset)
+{
+ switch (immed_size) {
+ case 1: *(s8 *)ptr = (s8) new_offset; break;
+ case 2: *(s16 *)ptr = (s16)new_offset; break;
+ case 4: *(s32 *)ptr = new_offset; break;
+ default: BUG();
+ }
+}
static void __init_or_module noinline
-apply_relocation(u8 *instr, size_t len, u8 *dest, u8 *src, size_t src_len)
+apply_relocation(u8 *insn_buff, size_t len, u8 *instr, u8 *repl, size_t repl_len)
{
struct insn insn;
int i = 0;
for (;;) {
- if (insn_decode_kernel(&insn, &instr[i]))
+ if (insn_decode_kernel(&insn, &insn_buff[i]))
return;
switch (insn.opcode.bytes[0]) {
@@ -229,20 +238,27 @@ apply_relocation(u8 *instr, size_t len, u8 *dest, u8 *src, size_t src_len)
case JMP8_INSN_OPCODE:
case JMP32_INSN_OPCODE:
case CALL_INSN_OPCODE:
- u8 *target = src + i + insn.length + insn.immediate.value;
- if (target < src || target > src + src_len) {
- apply_reloc(insn.immediate.nbytes,
- instr + i + insn_offset_immediate(&insn),
- src - dest);
- }
+ u8 *target = repl + i + insn.length + insn.immediate.value;
+ u8 *next_rip = instr + insn.length;
+ s32 new_offset;
+
+ if (instr < target)
+ new_offset = target - next_rip;
+ else
+ new_offset = next_rip - target;
+
+ apply_new_offset(insn.immediate.nbytes,
+ insn_buff + i + insn_offset_immediate(&insn),
+ new_offset);
+
}
if (insn_rip_relative(&insn)) {
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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