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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: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20231105213731.1878100-3-ubizjak@gmail.com
This commit is contained in:
Uros Bizjak 2023-11-05 22:34:36 +01:00 committed by Ingo Molnar
parent 43bda69ed9
commit 17bce3b2ae
3 changed files with 28 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/x86/include/asm/text-patching.h
View File

@ -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.

3
arch/x86/kernel/alternative.c
View File

@ -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;

32
arch/x86/kernel/callthunks.c
View File

@ -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;
}