Re: [PATCH 3/3] tracing/probes: Fix return value when "(fault)" is injected
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Date: 2023-07-07 02:02:18
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On Thu, 6 Jul 2023 09:50:39 -0400 Steven Rostedt [off-list ref] wrote:
quoted hunk ↗ jump to hunk
On Thu, 6 Jul 2023 13:40:36 +0900 Masami Hiramatsu (Google) [off-list ref] wrote:quoted
On Wed, 5 Jul 2023 22:49:56 -0400 Steven Rostedt [off-list ref] wrote:quoted
On Sun, 2 Jul 2023 23:47:35 +0900 "Masami Hiramatsu (Google)" [off-list ref] wrote:quoted
From: Masami Hiramatsu (Google) <mhiramat@kernel.org> When the "(fault)" is injected, the return value of fetch_store_string*() should be the length of the "(fault)", but an error code is returned. Fix it to return the correct length and update the data_loc according the updated length. This needs to update a ftracetest test case, which expects trace output to appear as '(fault)' instead of '"(fault)"'.Ah, because of patch 2, the ret < 0 makes it return without printing the "fault"?No, actually set_data_loc() updates the 'ret' argument, but it is just disposed... (not returned to the caller)That's not what I was talking about. We have: process_fetch_insn_bottom() { [..] case FETCH_OP_ST_STRING: loc = *(u32 *)dest; ret = fetch_store_string(val + code->offset, dest, base); break; [..] // And from patch 2 we have:@@ -193,6 +193,8 @@ process_fetch_insn_bottom(struct fetch_insn *code, unsigned long val, default: return -EILSEQ; } + if (ret < 0) + return ret; code++;And now that the return value of fetch_store_string() is being checked, and if it returns negative, it ends the function before being processed further. And if there's a fault, it happens to return negative! This patch now changes fetch_store_string() and fetch_store_string_user() to not return negative if there's a fault. As this patch has:@@ -107,9 +106,7 @@ fetch_store_string(unsigned long addr, void *dest, void *base) * probing. */ ret = strncpy_from_kernel_nofault(__dest, (void *)addr, maxlen); - set_data_loc(ret, dest, __dest, base, maxlen); - - return ret; + return set_data_loc(ret, dest, __dest, base, maxlen); }But to do that, you needed to update set_data_loc() to return a value. *that's* what I meant by 'Ah, because of patch 2, the ret < 0 makes it return without printing the "fault"?'
Yes, that's correct. Actually, the data ("(fault)") is stored, but ignored
because data_loc is not updated.
But wait, it seems that the print function shows (fault), so commit 2e9906f84fc7
("tracing: Add "(fault)" name injection to kernel probes") may not needed?
----
/* Print type function for string type */
int PRINT_TYPE_FUNC_NAME(string)(struct trace_seq *s, void *data, void *ent)
{
int len = *(u32 *)data >> 16;
if (!len)
trace_seq_puts(s, "(fault)");
else
----
In this case, what we need is to set data_loc length = 0 if ret < 0.
Do you really need to get '"(fault)"' (with double quotation) or
just '(fault)' (no double quotation) is OK?
Thank you,-- Stevequoted
-static nokprobe_inline void set_data_loc(int ret, void *dest, void *__dest, void *base, int len) +static nokprobe_inline int set_data_loc(int ret, void *dest, void *__dest, void *base, int len) { - if (ret >= 0) { - *(u32 *)dest = make_data_loc(ret, __dest - base); - } else { + if (ret < 0) { strscpy(__dest, FAULT_STRING, len); ret = strlen(__dest) + 1; } + + *(u32 *)dest = make_data_loc(ret, __dest - base); + return ret; } So this returns updated 'ret', and also update data_loc to use the updated 'ret' value (which is the length of the stored data).quoted
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>Thank you!quoted
-- Stevequoted
Fixes: 2e9906f84fc7 ("tracing: Add "(fault)" name injection to kernel probes") Cc: stable@vger.kernel.org Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> ---
-- Masami Hiramatsu (Google) [off-list ref]