From 669acc7eec223a81ea5e2420de85b61979ab7dad Mon Sep 17 00:00:00 2001 From: Nathan Lynch Date: Tue, 12 Dec 2023 11:01:50 -0600 Subject: [PATCH] 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)" Signed-off-by: Nathan Lynch Signed-off-by: Michael Ellerman Link: https://msgid.link/20231212-papr-sys_rtas-vs-lockdown-v6-3-e9eafd0c8c6c@linux.ibm.com --- arch/powerpc/kernel/rtas.c | 18 ++++++++++++++---- 1 file 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 */