Commit 17bce3b2 authored by Uros Bizjak's avatar Uros Bizjak Committed by Ingo Molnar
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x86/callthunks: Handle %rip-relative relocations in call thunk template 



Contrary to alternatives, relocations are currently not supported in
call thunk templates.  Re-use the existing infrastructure from
alternative.c to allow %rip-relative relocations when copying call
thunk template from its storage location.

The patch allows unification of ASM_INCREMENT_CALL_DEPTH, which already
uses PER_CPU_VAR macro, with INCREMENT_CALL_DEPTH, used in call thunk
template, which is currently limited to use absolute address.

Reuse existing relocation infrastructure from alternative.c.,
as suggested by Peter Zijlstra.

Signed-off-by: default avatarUros Bizjak <ubizjak@gmail.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20231105213731.1878100-3-ubizjak@gmail.com
parent 43bda69e

arch/x86/include/asm/text-patching.h

+2 −0
Original line number Diff line number Diff line
@@ -18,6 +18,8 @@ static inline void apply_paravirt(struct paravirt_patch_site *start, 
#define __parainstructions_end	NULL

#endif



void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len);



/*

 * Currently, the max observed size in the kernel code is

 * JUMP_LABEL_NOP_SIZE/RELATIVEJUMP_SIZE, which are 5.

arch/x86/kernel/alternative.c

+1 −2
Original line number Diff line number Diff line
@@ -325,8 +325,7 @@ bool need_reloc(unsigned long offset, u8 *src, size_t src_len) 
	return (target < src || target > src + src_len);

}



static void __init_or_module noinline

apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)

void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)

{

	int prev, target = 0;

arch/x86/kernel/callthunks.c

+25 −7
Original line number Diff line number Diff line
@@ -24,6 +24,8 @@ 


static int __initdata_or_module debug_callthunks;



#define MAX_PATCH_LEN (255-1)



#define prdbg(fmt, args...)					\

do {								\

	if (debug_callthunks)					\
@@ -184,10 +186,15 @@ static const u8 nops[] = { 
static void *patch_dest(void *dest, bool direct)

{

	unsigned int tsize = SKL_TMPL_SIZE;

	u8 insn_buff[MAX_PATCH_LEN];

	u8 *pad = dest - tsize;



	memcpy(insn_buff, skl_call_thunk_template, tsize);

	apply_relocation(insn_buff, tsize, pad,

			 skl_call_thunk_template, tsize);



	/* Already patched? */

	if (!bcmp(pad, skl_call_thunk_template, tsize))

	if (!bcmp(pad, insn_buff, tsize))

		return pad;



	/* Ensure there are nops */
@@ -197,9 +204,9 @@ static void *patch_dest(void *dest, bool direct) 
	}



	if (direct)

		memcpy(pad, skl_call_thunk_template, tsize);

		memcpy(pad, insn_buff, tsize);

	else

		text_poke_copy_locked(pad, skl_call_thunk_template, tsize, true);

		text_poke_copy_locked(pad, insn_buff, tsize, true);

	return pad;

}
@@ -297,20 +304,27 @@ void *callthunks_translate_call_dest(void *dest) 
static bool is_callthunk(void *addr)

{

	unsigned int tmpl_size = SKL_TMPL_SIZE;

	void *tmpl = skl_call_thunk_template;

	u8 insn_buff[MAX_PATCH_LEN];

	unsigned long dest;

	u8 *pad;



	dest = roundup((unsigned long)addr, CONFIG_FUNCTION_ALIGNMENT);

	if (!thunks_initialized || skip_addr((void *)dest))

		return false;



	return !bcmp((void *)(dest - tmpl_size), tmpl, tmpl_size);

	*pad = dest - tmpl_size;



	memcpy(insn_buff, skl_call_thunk_template, tmpl_size);

	apply_relocation(insn_buff, tmpl_size, pad,

			 skl_call_thunk_template, tmpl_size);



	return !bcmp(pad, insn_buff, tmpl_size);

}



int x86_call_depth_emit_accounting(u8 **pprog, void *func)

{

	unsigned int tmpl_size = SKL_TMPL_SIZE;

	void *tmpl = skl_call_thunk_template;

	u8 insn_buff[MAX_PATCH_LEN];



	if (!thunks_initialized)

		return 0;
@@ -319,7 +333,11 @@ int x86_call_depth_emit_accounting(u8 **pprog, void *func) 
	if (func && is_callthunk(func))

		return 0;



	memcpy(*pprog, tmpl, tmpl_size);

	memcpy(insn_buff, skl_call_thunk_template, tmpl_size);

	apply_relocation(insn_buff, tmpl_size, *pprog,

			 skl_call_thunk_template, tmpl_size);



	memcpy(*pprog, insn_buff, tmpl_size);

	*pprog += tmpl_size;

	return tmpl_size;

}