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| author | Nathan Lynch <nathanl@linux.ibm.com> | 2023-12-12 11:01:50 -0600 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2023-12-13 21:38:20 +1100 |
| commit | 669acc7eec223a81ea5e2420de85b61979ab7dad (patch) | |
| tree | b55a4e859ff92ea5b926b210fa478084eca1a33d | |
| parent | c500c6e736df030f8956080738f59701c0b43dd8 (diff) | |
| download | lwn-669acc7eec223a81ea5e2420de85b61979ab7dad.tar.gz lwn-669acc7eec223a81ea5e2420de85b61979ab7dad.zip | |
powerpc/rtas: Fall back to linear search on failed token->function lookup
Enabling any of the powerpc:rtas_* tracepoints at boot is likely to
result in an oops on RTAS platforms. For example, booting a QEMU
pseries model with 'trace_event=powerpc:rtas_input' in the command
line leads to:
BUG: Kernel NULL pointer dereference on read at 0x00000008
Oops: Kernel access of bad area, sig: 7 [#1]
NIP [c00000000004231c] do_enter_rtas+0x1bc/0x460
LR [c00000000004231c] do_enter_rtas+0x1bc/0x460
Call Trace:
do_enter_rtas+0x1bc/0x460 (unreliable)
rtas_call+0x22c/0x4a0
rtas_get_boot_time+0x80/0x14c
read_persistent_clock64+0x124/0x150
read_persistent_wall_and_boot_offset+0x28/0x58
timekeeping_init+0x70/0x348
start_kernel+0xa0c/0xc1c
start_here_common+0x1c/0x20
(This is preceded by a warning for the failed lookup in
rtas_token_to_function().)
This happens when __do_enter_rtas_trace() attempts a token to function
descriptor lookup before the xarray containing the mappings has been
set up.
Fall back to linear scan of the table if rtas_token_to_function_xarray
is empty.
Fixes: 24098f580e2b ("powerpc/rtas: add tracepoints around RTAS entry")
Reviewed-by: "Aneesh Kumar K.V (IBM)" <aneesh.kumar@kernel.org>
Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231212-papr-sys_rtas-vs-lockdown-v6-3-e9eafd0c8c6c@linux.ibm.com
| -rw-r--r-- | arch/powerpc/kernel/rtas.c | 18 |
1 files changed, 14 insertions, 4 deletions
diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c index ae9b10c954a1..f60a8e7bd5ed 100644 --- a/arch/powerpc/kernel/rtas.c +++ b/arch/powerpc/kernel/rtas.c @@ -572,11 +572,21 @@ static const struct rtas_function *rtas_token_to_function(s32 token) return NULL; func = rtas_token_to_function_untrusted(token); + if (func) + return func; + /* + * Fall back to linear scan in case the reverse mapping hasn't + * been initialized yet. + */ + if (xa_empty(&rtas_token_to_function_xarray)) { + for_each_rtas_function(func) { + if (func->token == token) + return func; + } + } - if (WARN_ONCE(!func, "unexpected failed lookup for token %d", token)) - return NULL; - - return func; + WARN_ONCE(true, "unexpected failed lookup for token %d", token); + return NULL; } /* This is here deliberately so it's only used in this file */ |