On 23/04/2025 10:22, Alexandre Ghiti wrote:
Hi Andy,On 07/04/2025 20:08, Andy Chiu wrote:From: Andy Chiu <[email protected]> We use an AUIPC+JALR pair to jump into a ftrace trampoline. Since instruction fetch can break down to 4 byte at a time, it is impossible to update two instructions without a race. In order to mitigate it, we initialize the patchable entry to AUIPC + NOP4. Then, the run-time code patching can change NOP4 to JALR to eable/disable ftrcae from a function. This limits the reach of each ftrace entry to +-2KB displacing from ftrace_caller. Starting from the trampoline, we add a level of indirection for it to reach ftrace caller target. Now, it loads the target address from a memory location, then perform the jump. This enable the kernel to update the target atomically. The new don't-stop-the-world text patching on change only one RISC-V instruction: | -8: &ftrace_ops of the associated tracer function. | <ftrace enable>: | 0: auipc t0, hi(ftrace_caller) | 4: jalr t0, lo(ftrace_caller) | | -8: &ftrace_nop_ops | <ftrace disable>: | 0: auipc t0, hi(ftrace_caller) | 4: nop This means that f+0x0 is fixed, and should not be claimed by ftrace, e.g. kprobe should be able to put a probe in f+0x0. Thus, we adjust the offset and MCOUNT_INSN_SIZE accordingly. Co-developed-by: Björn Töpel <[email protected]> Signed-off-by: Björn Töpel <[email protected]> Signed-off-by: Andy Chiu <[email protected]> --- Changelog v4: - Include Björn's fix for kprobe - Refactor code for better reading (Robbin, Björn) - Remove make_call_ra and friedns (Björn) - Update comments to match reality (Björn) - Drop code defined by !WITH_ARG - Add a synchronization point when updating ftrace_call_dest (Björn) --- arch/riscv/include/asm/ftrace.h | 49 ++++++------ arch/riscv/kernel/ftrace.c | 130 ++++++++++++++++---------------- arch/riscv/kernel/mcount-dyn.S | 9 +-- 3 files changed, 92 insertions(+), 96 deletions(-)diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.hindex d8b2138bd9c6..6a5c0a7fb826 100644 --- a/arch/riscv/include/asm/ftrace.h +++ b/arch/riscv/include/asm/ftrace.h @@ -20,10 +20,9 @@ extern void *return_address(unsigned int level); #define ftrace_return_address(n) return_address(n) void _mcount(void); -static inline unsigned long ftrace_call_adjust(unsigned long addr) -{ - return addr; -} +unsigned long ftrace_call_adjust(unsigned long addr); +unsigned long arch_ftrace_get_symaddr(unsigned long fentry_ip);+#define ftrace_get_symaddr(fentry_ip) arch_ftrace_get_symaddr(fentry_ip)/* * Let's do like x86/arm64 and ignore the compat syscalls. @@ -57,12 +56,21 @@ struct dyn_arch_ftrace { * 2) jalr: setting low-12 offset to ra, jump to ra, and set ra to * return address (original pc + 4) *+ * The first 2 instructions for each tracable function is compiled to 2 nop + * instructions. Then, the kernel initializes the first instruction to auipc at + * boot time (<ftrace disable>). The second instruction is patched to jalr to+ * start the trace. + * + *<Image>: + * 0: nop + * 4: nop + * *<ftrace enable>: - * 0: auipc t0/ra, 0x? - * 4: jalr t0/ra, ?(t0/ra) + * 0: auipc t0, 0x? + * 4: jalr t0, ?(t0) * *<ftrace disable>: - * 0: nop + * 0: auipc t0, 0x? * 4: nop * * Dynamic ftrace generates probes to call sites, so we must deal with @@ -75,10 +83,9 @@ struct dyn_arch_ftrace { #define AUIPC_OFFSET_MASK (0xfffff000) #define AUIPC_PAD (0x00001000) #define JALR_SHIFT 20 -#define JALR_RA (0x000080e7) -#define AUIPC_RA (0x00000097) #define JALR_T0 (0x000282e7) #define AUIPC_T0 (0x00000297) +#define JALR_RANGE (JALR_SIGN_MASK - 1) #define to_jalr_t0(offset) \ (((offset & JALR_OFFSET_MASK) << JALR_SHIFT) | JALR_T0) @@ -96,26 +103,14 @@ do { \ call[1] = to_jalr_t0(offset); \ } while (0) -#define to_jalr_ra(offset) \ - (((offset & JALR_OFFSET_MASK) << JALR_SHIFT) | JALR_RA) - -#define to_auipc_ra(offset) \ - ((offset & JALR_SIGN_MASK) ? \ - (((offset & AUIPC_OFFSET_MASK) + AUIPC_PAD) | AUIPC_RA) : \ - ((offset & AUIPC_OFFSET_MASK) | AUIPC_RA)) - -#define make_call_ra(caller, callee, call) \ -do { \ - unsigned int offset = \ - (unsigned long) (callee) - (unsigned long) (caller); \ - call[0] = to_auipc_ra(offset); \ - call[1] = to_jalr_ra(offset); \ -} while (0) - /*- * Let auipc+jalr be the basic *mcount unit*, so we make it 8 bytes here.+ * Only the jalr insn in the auipc+jalr is patched, so we make it 4 + * bytes here. */ -#define MCOUNT_INSN_SIZE 8 +#define MCOUNT_INSN_SIZE 4 +#define MCOUNT_AUIPC_SIZE 4 +#define MCOUNT_JALR_SIZE 4 +#define MCOUNT_NOP4_SIZE 4 #ifndef __ASSEMBLY__ struct dyn_ftrace; diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c index 1fd10555c580..cf78eef073a0 100644 --- a/arch/riscv/kernel/ftrace.c +++ b/arch/riscv/kernel/ftrace.c @@ -8,10 +8,21 @@ #include <linux/ftrace.h> #include <linux/uaccess.h> #include <linux/memory.h> +#include <linux/irqflags.h> #include <linux/stop_machine.h> #include <asm/cacheflush.h> #include <asm/text-patching.h> +unsigned long ftrace_call_adjust(unsigned long addr) +{ + return addr + MCOUNT_AUIPC_SIZE; +} + +unsigned long arch_ftrace_get_symaddr(unsigned long fentry_ip) +{ + return fentry_ip - MCOUNT_AUIPC_SIZE; +} +Those functions cause the following errors when building with !CONFIG_DYNAMIC_FTRACE, but I'm not sure how to fix this:../arch/riscv/kernel/ftrace.c: In function 'ftrace_call_adjust':../arch/riscv/kernel/ftrace.c:19:35: error: 'MCOUNT_AUIPC_SIZE' undeclared (first use in this function)19 | return addr + 8 + MCOUNT_AUIPC_SIZE; | ^~~~~~~~~~~~~~~~~../arch/riscv/kernel/ftrace.c:19:35: note: each undeclared identifier is reported only once for each function it appears inCC fs/9p/vfs_dir.o ../arch/riscv/kernel/ftrace.c: In function 'arch_ftrace_get_symaddr':../arch/riscv/kernel/ftrace.c:26:28: error: 'MCOUNT_AUIPC_SIZE' undeclared (first use in this function)26 | return fentry_ip - MCOUNT_AUIPC_SIZE; | ^~~~~~~~~~~~~~~~~ CC drivers/pci/pcie/pme.o ../arch/riscv/kernel/ftrace.c: In function 'ftrace_call_adjust':../arch/riscv/kernel/ftrace.c:22:1: error: control reaches end of non-void function [-Werror=return-type]22 | } | ^ ../arch/riscv/kernel/ftrace.c: In function 'arch_ftrace_get_symaddr':../arch/riscv/kernel/ftrace.c:27:1: error: control reaches end of non-void function [-Werror=return-type]27 | } | ^ cc1: some warnings being treated as errorsmake[5]: *** [../scripts/Makefile.build:203: arch/riscv/kernel/ftrace.o] Error 1
So I fixed those errors with the following, let me know if that's not correct:
diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index d65f06bfb4573..4c6c24380cfd9 100644
--- a/arch/riscv/kernel/ftrace.c
+++ b/arch/riscv/kernel/ftrace.c
@@ -13,6 +13,7 @@
#include <asm/cacheflush.h>
#include <asm/text-patching.h>
+#ifdef CONFIG_DYNAMIC_FTRACE
unsigned long ftrace_call_adjust(unsigned long addr)
{
if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS))
@@ -26,7 +27,6 @@ unsigned long arch_ftrace_get_symaddr(unsigned long
fentry_ip)
return fentry_ip - MCOUNT_AUIPC_SIZE;
}
-#ifdef CONFIG_DYNAMIC_FTRACE
void arch_ftrace_update_code(int command)
{
mutex_lock(&text_mutex);
@@ -191,7 +191,12 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
return 0;
}
-#endif
+#else /* CONFIG_DYNAMIC_FTRACE */
+unsigned long ftrace_call_adjust(unsigned long addr)
+{
+ return addr;
+}
+#endif /* CONFIG_DYNAMIC_FTRACE */
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
Thanks,
Alex
#ifdef CONFIG_DYNAMIC_FTRACE void ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex) {@@ -32,51 +43,32 @@ void ftrace_arch_code_modify_post_process(void) __releases(&text_mutex)mutex_unlock(&text_mutex); } -static int ftrace_check_current_call(unsigned long hook_pos, - unsigned int *expected)+static int __ftrace_modify_call(unsigned long source, unsigned long target, bool validate){ + unsigned int call[2], offset; unsigned int replaced[2]; - unsigned int nops[2] = {RISCV_INSN_NOP4, RISCV_INSN_NOP4}; - /* we expect nops at the hook position */ - if (!expected) - expected = nops; + offset = target - source; + call[1] = to_jalr_t0(offset); - /* - * Read the text we want to modify; - * return must be -EFAULT on read error - */ - if (copy_from_kernel_nofault(replaced, (void *)hook_pos, - MCOUNT_INSN_SIZE)) - return -EFAULT; - - /* - * Make sure it is what we expect it to be; - * return must be -EINVAL on failed comparison - */ - if (memcmp(expected, replaced, sizeof(replaced))) { - pr_err("%p: expected (%08x %08x) but got (%08x %08x)\n", - (void *)hook_pos, expected[0], expected[1], replaced[0], - replaced[1]); - return -EINVAL; + if (validate) { + call[0] = to_auipc_t0(offset); + /* + * Read the text we want to modify; + * return must be -EFAULT on read error + */+ if (copy_from_kernel_nofault(replaced, (void *)source, 2 * MCOUNT_INSN_SIZE))+ return -EFAULT; + + if (replaced[0] != call[0]) { + pr_err("%p: expected (%08x) but got (%08x)\n", + (void *)source, call[0], replaced[0]); + return -EINVAL; + } } - return 0; -} --static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target,- bool enable, bool ra) -{ - unsigned int call[2]; - unsigned int nops[2] = {RISCV_INSN_NOP4, RISCV_INSN_NOP4}; - - if (ra) - make_call_ra(hook_pos, target, call); - else - make_call_t0(hook_pos, target, call); -- /* Replace the auipc-jalr pair at once. Return -EPERM on write error. */ - if (patch_insn_write((void *)hook_pos, enable ? call : nops, MCOUNT_INSN_SIZE))+ /* Replace the jalr at once. Return -EPERM on write error. */+ if (patch_insn_write((void *)(source + MCOUNT_AUIPC_SIZE), call + 1, MCOUNT_JALR_SIZE))return -EPERM; return 0;@@ -84,22 +76,21 @@ static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target,int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) { - unsigned int call[2];+ unsigned long distance, orig_addr, pc = rec->ip - MCOUNT_AUIPC_SIZE;- make_call_t0(rec->ip, addr, call); - - if (patch_insn_write((void *)rec->ip, call, MCOUNT_INSN_SIZE)) - return -EPERM; + orig_addr = (unsigned long)&ftrace_caller; + distance = addr > orig_addr ? addr - orig_addr : orig_addr - addr; + if (distance > JALR_RANGE) + return -EINVAL; - return 0; + return __ftrace_modify_call(pc, addr, false); } -int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, - unsigned long addr)+int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr){ - unsigned int nops[2] = {RISCV_INSN_NOP4, RISCV_INSN_NOP4}; + u32 nop4 = RISCV_INSN_NOP4; - if (patch_insn_write((void *)rec->ip, nops, MCOUNT_INSN_SIZE)) + if (patch_insn_write((void *)rec->ip, &nop4, MCOUNT_NOP4_SIZE)) return -EPERM; return 0;@@ -114,21 +105,38 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,*/ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec) { - int out; + unsigned long pc = rec->ip - MCOUNT_AUIPC_SIZE; + unsigned int nops[2], offset; + int ret; + + offset = (unsigned long) &ftrace_caller - pc; + nops[0] = to_auipc_t0(offset); + nops[1] = RISCV_INSN_NOP4; mutex_lock(&text_mutex); - out = ftrace_make_nop(mod, rec, MCOUNT_ADDR); + ret = patch_insn_write((void *)pc, nops, 2 * MCOUNT_INSN_SIZE); mutex_unlock(&text_mutex); - return out; + return ret; } +ftrace_func_t ftrace_call_dest = ftrace_stub; int ftrace_update_ftrace_func(ftrace_func_t func) { - int ret = __ftrace_modify_call((unsigned long)&ftrace_call, - (unsigned long)func, true, true); - - return ret; + WRITE_ONCE(ftrace_call_dest, func); + /*+ * The data fence ensure that the update to ftrace_call_dest happens + * before the write to function_trace_op later in the generic ftrace. + * If the sequence is not enforced, then an old ftrace_call_dest may + * race loading a new function_trace_op set in ftrace_modify_all_code+ *+ * If we are in stop_machine, then we don't need to call remote fence+ * as there is no concurrent read-side of ftrace_call_dest. + */ + smp_wmb(); + if (!irqs_disabled()) + smp_call_function(ftrace_sync_ipi, NULL, 1); + return 0; } struct ftrace_modify_param { @@ -172,17 +180,11 @@ void arch_ftrace_update_code(int command) int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, unsigned long addr) { + unsigned long caller = rec->ip - MCOUNT_AUIPC_SIZE; unsigned int call[2]; - unsigned long caller = rec->ip; - int ret; make_call_t0(caller, old_addr, call); - ret = ftrace_check_current_call(caller, call); - - if (ret) - return ret; - - return __ftrace_modify_call(caller, addr, true, false); + return __ftrace_modify_call(caller, addr, true); } #endifdiff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.Sindex 3f06b40bb6c8..8aa554d56096 100644 --- a/arch/riscv/kernel/mcount-dyn.S +++ b/arch/riscv/kernel/mcount-dyn.S @@ -13,7 +13,6 @@ .text -#define FENTRY_RA_OFFSET 8 #define ABI_SIZE_ON_STACK 80 #define ABI_A0 0 #define ABI_A1 8 @@ -62,8 +61,7 @@ * After the stack is established, * * 0(sp) stores the PC of the traced function which can be accessed -* by &(fregs)->epc in tracing function. Note that the real -* function entry address should be computed with -FENTRY_RA_OFFSET. +* by &(fregs)->epc in tracing function. * * 8(sp) stores the function return address (i.e. parent IP) that * can be accessed by &(fregs)->ra in tracing function. @@ -140,7 +138,7 @@ .endm .macro PREPARE_ARGS - addi a0, t0, -FENTRY_RA_OFFSET + addi a0, t0, -MCOUNT_JALR_SIZE // ip (callsite's jalr insn) la a1, function_trace_op REG_L a2, 0(a1) mv a1, ra @@ -153,7 +151,8 @@ SYM_FUNC_START(ftrace_caller) PREPARE_ARGS SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL) - call ftrace_stub + REG_L ra, ftrace_call_dest + jalr ra, 0(ra) RESTORE_ABI_REGS bnez t1, .Ldirect_______________________________________________ linux-riscv mailing list [email protected] http://lists.infradead.org/mailman/listinfo/linux-riscv
